My ex is one of my closest friends. We split seven years ago after a two-year relationship, but we, and our families, are still close. She even organised my last birthday party. And it seems I’m not alone – everywhere you look, from Gwyneth Paltrow and Chris Martin’s “conscious uncoupling” to Prince Andrew and Fergie’s rumoured cohabitation and “friends with benefits” situation, to actor Michael Sheen’s ex Kate Beckinsale comforting him through his latest breakup, people who were once romantically involved have renegotiated their relationships and become friends instead.

No one pretends it’s easy. “A breakup can be worse than a bereavement,” says Miles Pulver, a relationship therapist. “When someone has died, they are gone for ever, whereas with an ex they’re still alive and may be with someone else. You have to grieve the loss and watch them move on without you.” Perhaps this is why, he says, so many people are determined to remain friends. “We have an attachment system within us which means we need to stay close to people and resist unbonding.” In my case, that resistance involved a bereavement (of my mother), a conscious unbonding (six months of my ex travelling abroad) and certainly no “benefits” – except the occasional family dinner. It’s a situation that still confounds our mutual friends, with reactions ranging from envy to disbelief, but it works for us.

For Joy Smith, 37, becoming friends with Joe, her ex of eight years, was similarly fraught. Their relationship broke down in 2004 when he cheated on her with her best friend’s cousin, at which point things seemed unsalvageable. “It was awful. I would see Joe’s sister, who I was good friends with, and just be crying all the time,” she says. “I still had feelings for him so if he’d said he wanted to give things another go, I probably would have.”

It wasn’t until Christmas, a few months later, that Smith decided to move on. “We were such good friends at school before we got together; there was a point where I couldn’t be bothered to be angry any more,” she says. “He had apologised a lot, it was clear that we weren’t going to get back together, so I wanted to be friends because it would have been too difficult to stay in touch with our mutual friends otherwise.”

‘I realised that I’d much rather have Joe as a friend than not have him in my life at all’ ... Joy Smith. Photograph: Graeme Robertson/The Guardian

Things were helped by the fact that Smith soon met her future husband, Luke, at Joe’s sister’s 21st birthday – a party where Joe and Smith ended up “having” to share a bed. “Luke found my friendship with Joe really difficult at the beginning,” Smith says. “Joe still knew me better than anyone else, so that would have been threatening.” Yet, persistence and distance – namely, no more bed-sharing – paid off. “It was really hard, but I realised that I’d much rather have Joe as a friend than not have him in my life at all, so that was something we had to work out,” she says. “And Luke realised there was nothing to worry about as our own relationship strengthened.” Five years later, Joe was a witness at their wedding. “He’s like a brother to me now; I love him to pieces, but I’m not in love with him.”

Perhaps time heals all wounds, but for those with breakups in the more recent past, becoming friends can seem more difficult. “I don’t think you can segue from a passionate relationship into a friendship without there being quite a big gap,” Christina Fraser, a relationship counsellor, says. “You have to be careful because some people can’t face an ending, so they say: ‘Let’s be pals’, but they don’t really mean it.”

After Mari Thomson, 25, ended her four-year relationship with Will, in 2016, she left her job, went to China for six months and cut off contact. “We were together all through university, but by the end, the romance was gone and it felt like we were just friends,” Thomson says. When she returned, she wanted to explore her sexuality further and started dating women.

“I’d had a relationship with another woman when I was younger and it was at the back of my mind when Will and I broke up,” she says. “I wanted to revisit that to see what it would be like.” Such a seemingly abrupt change caused difficulties for her relationship with Will. “During that transition period, there were some really tough moments,” she says. “We’d be at the same parties and be wondering who the other person was getting with, or we’d be getting too close; it was confusing.”

With time though, things settled. “Luckily, nothing really bad happened during the breakup so maybe it was easier to be friends,” Thomson says. “I feel really fortunate that we’ve managed it. I’m so happy for him and he is for me too.”

There is, though, the danger of becoming too close once the relationship has ended, counsellor Barbara Bloomfield says. “There is a risk that you stifle the capacity to move on if you’re still very close to your ex,” she says. “It can create the feeling that there are three people in the relationship.”

When it comes to parenting and the wellbeing of children, sensible contact is, of course, the ideal. For Gina Decio, 36, and Rob Carter, 41, in fact, the ambition to be on good terms for the sake of their nine-year-old daughter caused their divorce, one month after they celebrated their tenth anniversary. “By the end of our relationship, we were more like housemates than husband and wife,” Decio says. “We drew up a Google document with options on how we could work things out. Our ultimate goal was to be laughing and dancing together for our daughter’s 30th birthday.”

After a month, the options were whittled down to two. Plan A was relationship therapy – which “would cost a lot of money and might not get the desired results”, Carter remembers writing – while plan B was to split up. They chose B, and two years later Decio and Carter see each other “at least three times a week” and “speak almost every day”.

It’s clear Decio and Carter have a good co-parenting relationship – they joke and chat as well as deal with all the necessary scheduling. “We dealt with things very openly,” Decio says. “While the practicalities of splitting up were hard, the main thing is that we’ve stayed consistent for our daughter. We still go to London zoo for her birthday and take the same pictures together.”

When I was with my second husband, we would meet up for dinner with my first husband every Tuesday Helen Meissner

In fact, the pair spent last Christmas with Carter’s extended family and Decio’s new partner. “Watching Gina’s boyfriend chatting with my aunt was very funny,” Carter says. “We want to keep doing things together, like planning a big holiday and spending all our birthdays as a family.” Thinking of Bloomfield’s advice, I ask if this closeness risks alienating new partners. “Look, if we wanted to be together again, we would never have broken up in the first place,” Carter says. “We’ve already been through the process and we don’t want to do it again. Our friendship is the most important thing for our daughter and our partners understand that.”

When it comes to maintaining relationships with exes, Helen Meissner, 52, is the most experienced of my interviewees. Having just gone through a divorce with her fourth husband, she remains on good terms with three. “When I was with my second husband, Stephen, we would meet up for dinner with my first husband every Tuesday,” Meissner says. “That went on for 10 years.”

That level of friendship is surely unattainable for most, though? “You need to step aside from your ego,” Meissner says. “You’ve created a situation which society doesn’t like – choosing to end a relationship – and if you throw away your relationship, you endanger your shared memories, and that’s all you have in life.”

Stephen adds that the fact that he and Helen met while working together provided a foundation for a strong relationship after the breakup. “We’re very similar people – probably too similar – but it meant that after the romance died, the friendship developed naturally.” This friendship included going on holiday with their two children and Stephen’s ex-wife and her three children – and staying in adjoining rooms.

A symbol of their continued relationship is their son’s graduation photo from last year, which Helen proudly shows me. “Just me and Stephen went together to see him,” she says. “That can be quite tricky when you both have new partners, but we’ve made it work. Our son, Lewis, actually posted that picture on his Facebook page; he was proud that both of his parents came to his graduation.”

The common thread in these friendships seems to be the understanding from both parties that their romance is well and truly over. “Relationships that do not end peacefully do not end at all,” Pulver says. “If you give yourself time to grieve and honour your relationship, that leaves the heart more free to form new bonds – as friends with your ex and [romantically] with other people, without resentments.” Whether it’s witnessing your ex’s wedding, co-parenting your children or going on joint holidays, “having a free heart is the best thing you can do,” Pulver says. “And if you can achieve that with ones you have loved, surely there is no more admirable a way to live life.”