Getting married used to mean a promise of 40 years, if you were lucky increased life expectancy means it could be much longer. Will your relationship go the distance?

My boyfriend looks terrible for his age. His skin feels as fragile and wrinkled as used clingfilm; age spots pepper his face and arms. What hair he still has is faded to grey, and the laughter we have shared over the years has etched itself in the lines around his eyes. Mind you, I dont look too hot, either. We have both been transformed by a makeup artist who, with latex and face paint, has fast-forwarded us from partners of four years into husband and wife of 60 years. It is a very odd experience; I feel a flash of nostalgia for 30-year-old me, and immediately feel the urge to wear a bikini. Its like an injection of Nora Ephron: Oh, how I regret not having worn a bikini for the entire year I was 26. If anyone young is reading this, go, right this minute, put on a bikini, and dont take it off until youre 34.

These pictures are the result of an experiment. I wanted to explore a question that pricks the minds of many couples at our life stage. We are both 30; a year and a half ago we bought a flat together; we have started to think about marriage. Perhaps the phrase started to think is disingenuous; the truth is, Shaun grew so bored with my talking about it that he banned me from mentioning it until after Euro 2016.

And so we find ourselves on the brink of a lifelong commitment, poised to make the same promise made by our parents, our grandparents and our great-grandparents, stretching back as far as our family trees will go, into countries I have never visited, from Yemen to Poland. But if and when we make that same promise, it will mean something very different. Because when our ancestors swore to love each other unto death, that meant 40 years together, if they were lucky. For us, thanks to improvements in healthcare and life expectancy (currently 79 for men and 83 for women in England and Wales, and set to rise), it could be more like 60 years. This is a radical shift, and one that forces us to question our assumptions about commitment and love. What does the age of longevity mean not just for individual marriages, but for the institution of marriage itself? What does it mean to say, Till death do us part in 2016?

As our life expectancy has improved (more than one-third of babies born today could live to 100), so have our expectations: we want a marriage to be great, not just good enough, all the way to the end. Dr Helen Fisher has been researching this issue for 40 years, and recently published an updated edition of her book Anatomy Of Love: A Natural History Of Mating, Marriage And Why We Stray. The focus of modern marriage is not stability, its love, she says. A century ago, a woman wouldnt have ended a marriage that was satisfactory, but a recent survey showed that one-third of people would leave a satisfactory marriage if they werent in love with their partner. Today, we want it all, and well walk away if we dont have it.

And so to the rise of the grey divorce. Recent figures from the Office for National Statistics show divorce is falling in all age groups in the UK except for the over-50s, among whom it has risen by nearly 11% in a decade. Nearly 60,400 people in this demographic divorced in England and Wales in 2013, while the overall number of divorces fell to a 40-year low. The same trend has also been observed in the US, where in 2014 those aged 50 and over were twice as likely to go through a divorce than in 1990; the increase was even higher for those over 64.

I have always assumed that the grey part of marriage was the best bit. I watch with loving envy as my parents enter their fifth decade together, finally allowed to relax and enjoy themselves after all the child-rearing and careering and work-life balancing. But, for many, decades of marriage can simply bring boredom that feeling of, Is this all there is? Of meh.

Roger Jenkins, 68, ended his 33-year marriage at the age of 65. For me, as for a lot of people, crunch time in a relationship comes when you retire, he says. Suddenly the person you saw for a couple of hours each night, mostly spent in front of the telly, you are now seeing 24/7. And all the problems, which you saw for only a few hours a week, you now see 24/7, too. My wife had a great social life, and when I finally retired and wanted a holiday, she said, No, I have my own life. I dont want to go around with you all the time.

After trying marriage counselling and discussing the situation with his children, both in their 30s, Roger filed for divorce. It was not an easy decision he had to overcome the stigma he had absorbed as a boy: People of my generation grew up at a time when divorce was virtually unknown and viewed as terribly sinful. That burrows into your psyche at a fairly early age. But a lot of people my age are fit and reasonably affluent, because theyve had the benefit of a property boom, and its now easier to get divorced than it used to be so why should I spend the rest of my life in misery?

Relate counsellor Barbara Bloomfield agrees: Women and men are feeling so much younger than they did in previous generations, and they fervently believe they have 30 more years after retirement. Some think, why stick with the same old same old if you might be able to find someone better?

Older couples have always had to deal with an onslaught of potentially stressful factors: boredom, yes, but also hormonal changes that can lead to mismatched sex drives, children leaving home, retirement. Bloomfield explains: There are quite a few mothers and fathers who cant get used to being a couple after children have left home and they have stopped working, when theyre under each others feet all day. Either the marriage crumbles or they find a new way to be together. But people are refusing to accept these changes as inevitable even at 80, because five, 10 years is too long if you are unhappy.

Divorce lawyer Kerry Russell says she has seen many couples like Roger and his ex-wife. The main trend I have seen is couples divorcing due to the realisation that there is more in life. They sometimes describe their marriage as tedious, and many feel trapped in a routine. They often care very much for their spouse, but the differences between them seem more apparent. They see divorce as a way to gain some independence and live life to the full.

Moya
Will you still love me tomorrow? Moya and Shaun reimagined. Photograph: David Yeo for the Guardian

Roger met his new partner through work two years ago. Were blissfully happy, he says. Sixty is the new 50 were not old gits, we love life, we travel. Im deeply in love with my partner and looking forward to spending the rest of my life with her.

After speaking to Roger, I find myself questioning my naive, unmarried assumptions about what constitutes a failed marriage. Can you really consider two children, 30 years together, an amicable end and a second happy relationship a failure?

For Fisher, the rising divorce rates among the over-50s represent one part of a sea change. She says, I think the concept of till death do us part is going by the way. What were going to see is serial monogamy, a series of pair bonds. Much of marriage as we know it we owe to the agrarian revolution, she argues: On the farm, you had to marry the right girl, from the right kin connection, from the right social standing, and hopefully from the farm next door. And you really had to stay married for life because you couldnt leave the farm.

She thinks well have more civil unions, and that it will become easier to marry and easier to divorce. Does this mean well drop that line, till death do us part? No, were very schmaltzy people. And theres something called cultural lag: our marriage habits may change much more rapidly than our marriage belief systems. So even though a great many people dont really know if it will be forever, theyll use the term, and have it in their heads, along with a whole lot of hopes and dreams.

Jessica Graham sees this as a positive development. She married her ex-husband at 22 and divorced at 52, 10 years ago. They got engaged a few months after meeting, and this, she suggests, is another reason for the spike in divorce among the over-50s. A speedy engagement is more unusual now: this wasnt true of her generation of grey divorcees back when they were lustrous newlyweds.

Jessica is a fiercely intelligent, witty, compassionate woman, a proud northerner with a sense of humour. She cant recall any happy times from her marriage. So why did she wait 30 years? Her answer she wanted to protect her daughters is another explanation for the increase in later-life divorce, and reminds me of the punchline of a dark joke: a 96-year-old is asked by his divorce lawyer, why did you wait so long? He replies, We wanted to wait until the children had died.

Jessica tells me, You feel bound to it, so you carry on, grit your teeth and stay married, despite it being very, very unhappy. My daughters grew up in a mild war zone; I look back and wish they hadnt had to experience it. She had planned to delay divorce until her daughters went to university, but they intervened earlier.

When I ask if she wants to meet someone else, Jessica is adamant in her refusal. I am happy being single, and financially secure. I like being able to do pretty well what I want, when I want. I can commute to London, go to the theatre, to concerts. Although she felt lonely to start with, she says, I felt lonelier in my marriage than I do now. What is the hardest thing about her situation? I dont find anything hard right now. Im OK. And yet: I wouldnt say Im yabadabadoo happy, and I dont think I ever will be. She thinks this is because that kind of happiness comes from sharing a life with someone.

As plan Bs go, there are far worse, says relationship psychologist Susan Quilliam. I would argue that the best option is a happy partnership, but the next best option is happy singledom. Ive known many friends and clients who are much happier now that theyre not in their relationship. Of course, there are single people who are unhappy without a companion, but from what Ive seen, the unhappiest option is an unhappy marriage, because you dont just have yourself to cope with.

When I speak to Lucy Taylor, 59, she seems politely, quietly, yabadabadoo happy. After her divorce, she swore she would never marry again. She was traumatised by the breakdown of her marriage. Her then husband called her his soul mate, and she believed him. Then he came home from work one evening and said he had fallen in love with somebody else, and wanted to be with her. The door opened, the grenade rolled in, then the door was closed.

Her husband was a corporate high flyer, and Lucy worked part-time in IT while their son was young, before returning to full-time work as a facilities manager. She was 46 when they divorced. It was shocking, devastating. When you meet somebody that you really care for, they give you a piece of their soul. And when they leave, they take that part back. You feel as if youve been amputated from their life.

In some ways, I despise myself because it took me so long to get over him years and years. It was a scary, lonely time. When you have loved deeply, its very difficult to trust people. Thats why I said I would never marry again. Because to intertwine your heartstrings and your finances with somebody elses, well, the prospect of being hurt or abandoned again is in the background of your mind all the time.

She met Joe at a dance class a couple of years after the divorce. Their first date was a lunch that lasted 12 hours, but she wanted to take things very, very slowly. Over a number of years, and with the blessing of her daughter, Joe moved in one sock at a time. They married two years ago, when Lucy was 57.

She still believes in marriage, and that you have to give it everything, even if it may fail. Joe and I didnt have a pre-nup that was my choice, against my solicitors advice. I felt its not a great way to start a marriage, if youre immediately saying I dont trust you. When we made our vows, I absolutely thought, I want to be with this man, I will always be good to him and I wont betray him. I loved hard and I lost, and Im loving hard again. And, hopefully, thats the way it will end, and we will die in each others arms. Thats what I would like.

The happy marriage is so ingrained in us as the only acceptable happy ending, from Shakespeare to When Harry Met Sally, that many of us (myself included) must subconsciously absorb the idea that any other ending is a failure. When I was younger, I never thought I would get married. Its just a piece of paper, I would say. I wanted my partner to wake up every morning and choose to stay with me because he wanted to, not because of some promise he had made decades earlier. But as the years have passed, and Ive cried at the weddings of so many friends, and watched my parents grow old, Ive come to feel differently. I see the value that these pieces of paper have in our lives passports, birth certificates, job contracts; these documents mark out the minutiae and the momentous in our lives, and marriage is both of those. I want our names to be written next to each other in that register, for them to be buried deep in the council archives, gathering dust. But perhaps I need to be more open-minded.

Emily White, 72, cast a light on the assumptions I never knew I had about finding happiness in old age: it doesnt have to mean going to bed with your husband every night. She was a widow when she met her second husband, but 11 years into that marriage, she realised he had transformed into a Jekyll and Hyde character. She divorced him four years ago and, she says, Im much happier now. Ive got a new partner, hes 77, and I get ruined rotten he takes me out for dinner every Saturday night. I keep getting told by my daughter that I have a better social life than she does. Im in the University of the Third Age, Im in a history group. I go to keep fit and do all sorts of daft things. When youre over 70, you can decide for yourself what you do. My partner and I each have our own houses, and we have a great time. I get a phone call every night, but we dont get under each others skin.

Its never too late to find an expression of love that works for you, and that may well not involve marriage. Sue Andrews, partner at the law firm BP Collins, has 35 years experience in family law and has represented many older clients, ranging in age up to their 90s: It was lovely to be told by an elderly client that I had enabled them to enjoy the rest of the time they had left, she says.

But there is also a darker side, especially at a time when loneliness among the elderly is such a compelling issue. Ruth Langford, community manager at Wikivorce, a social network for people in the UK going through divorce, says this year she has spoken to more people divorcing in their 70s and 80s than ever before. Its quite sad. These are people who have been married for 60 years, who should be enjoying their remaining years in peace and comfort, instead of entering into a legal situation that is fraught with emotional distress and expense. Langford says divorce for older people can be even more painful than it is for younger couples: It can often be a very lonely experience, losing long-term friends and causing family members to fall out. Often the disputes are over things of sentimental rather than real value, such as photograph albums of their children and grandchildren.

All the people I spoke to told me they married for life, all of them got divorced, and not one of them felt he or she was to blame. This is an alarming thing to hear when you are thinking about getting married yourself. No matter how fiercely you believe in your relationship, no matter how much you love your partner, you cannot see into the future, especially 80 years ahead; you cannot know for certain if boredom, unhappiness or personality changes will mean you are parted not by death but before. You have to take a punt. But I am comforted by Susan Quilliam, who tells me, In some ways, longer life expectancy is a threat; in others, its a huge opportunity, because unless youre very unlucky or closed and unreflective, your later life relationships can be better. They can be worse because of the Pandoras box of baggage you bring with you. But they can also be informed by the wisdom you bring.

Most of my interviewees felt no regrets about marrying their partners; they saw the value in the happy times they had spent together, the children they had raised. Jessica Graham felt she had failed because she had broken her vows, but she thinks a younger generation wont feel that: Younger people have the confidence to hold their hands up and say, it isnt a failure, it just hasnt worked.

After speaking to so many people about why their marriage ended, I feel less afraid of commitment. The desire to get married remains a gut instinct. I think Fisher gets closest to explaining why: I have studied the brain circuitry for romantic love and marriage, and these brain systems arent going to die. They evolved more than 4m years ago, and theyll be with us, if our species survives on the planet, for another 4m. The drive to fall in love and form a pair bond, rear your children as a team and make it a socially sanctioned relationship through marriage is not going to go away.

So what did I see at that photoshoot, when Shaun came out of makeup? My voice caught in my throat, in a rush of emotion I hadnt expected. I saw the man I love, but a future version of him, softer around the edges. He looked kind and wise and handsome, and, if I squinted a little (OK, a lot), a bit like George Clooney. I thought, I want to grow old with you. A week later, Shaun bought me a bunch of flowers. Inside the flowers was a photograph of us, and a postcard. On the postcard he had written a funny little poem, including the lines, Since you make me, and I hope I make you, just as happy as Larry, how about we marry? I felt terrified and overwhelmingly happy. Perhaps it was my age spots that made him forget about Euro 2016; well never know. All we can do, like the generations before us, is take our chance.

Some names have been changed.

How to stay together, for ever: relationship therapist Andrew G Marshalls advice

Learn how to argue
We have this idea that we will find a soul partner who will agree with us on everything. This is a myth and often makes people feel that they are not allowed to disagree with their partner, which can be disastrous. The important phrase is, I can ask, you can say no, and we can negotiate. Argue about one thing at a time. Dont attack your partners personality, and dont bottle everything up, because one day it will all come pouring out. People sometimes have affairs because they havent had their needs met. But remember that you must articulate what those needs are.

Embrace change
Accept that, even after 35 years of marriage, your partner might change in ways you never expected. I think couples should go out every 10 years and have a first date again to meet the new person theyre married to. Ask your partner, What are your hopes and dreams? They may not be what you expect. Dont let this make you anxious. Be open to finding out that your partner isnt exactly as you had imagined.

Have separate interests
Spending periods of time apart studying or travelling or having different hobbies can bring energy back into the relationship. Its important to have joint endeavours, but make time to be apart, too. If you stop your partner doing what they want, it makes your relationship vulnerable.

Make each other a priority
What often happens is that after retirement, or when children leave home, a couple realise that they have been on separate train tracks for years. It was just hidden by the business of life. Family time and couple time are two totally different things. You might think that your partner will understand if you ignore them for 25 years and focus on your children. But if you feel bottom of the pecking order, it can get to you.

Flirt
We often tell people what we dont like, but were bad at communicating the positives. Flirting with each other is fabulous. It shows you care. You need to learn how to touch each other, too. Make sure it doesnt only happen when initiating sex. Make time to hug and kiss and stroke each other. It keeps you feeling connected.

Appreciate the magic
When talking about newlyweds, people often say, Its all downhill from here. I disagree. Yes, falling in love is beautiful, but after more than 35 years together it can be just as magical as when you first met. At first its about the promise of a life together. Later on, its about the reality of the life you have made together. What could be more romantic than that?

Andrew G Marshall is author of I Love You But Im Not In Love With You: Seven Steps To Saving Your Relationship.

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