For 40-year-old Anne, the 10 years she has spent with her partner have been defined by betrayal. “A year into what I considered to be a near-perfect relationship, I found out Patrick had had an affair and that the woman was pregnant,” she says. “That child is now like my own and, although we initially split for a few months, Patrick and I have stayed together. People might find it strange but the affair made us closer and I love him now more than ever.”

Staying close after such a colossal betrayal may seem impossible, yet the relationship therapist Andrea Tibbitts has seen many similar situations. She believes betrayal can enhance a relationship if dealt with correctly. “I see it as an opportunity to take the relationship to the next level,” she says. “If both parties can gain closure and the betrayer takes responsibility for their actions, it can mark the end of a damaging relationship and the start of a new, more open and communicative partnership.”

I wish we could change our preconceptions that unfaithfulness is something not to be forgiven Sienna

Obviously, those are big “ifs”. “The affair left me feeling totally inadequate,” says Anne, who found out what was going on after glimpsing a text message on Patrick’s phone. “I had to deal with low self-esteem afterwards. We separated for a couple of months, but it showed him how much he needed me. I needed more appreciation from him to continue in the relationship and strangely the affair provided that – it pushed us to go into couples therapy and address the things he was taking for granted, as well as putting boundaries in place for something like this to never happen again. We’ve been very attentive to each other’s needs ever since.”

These “boundaries” include Anne’s demand that Patrick not spend time alone with the mother of his child, and that Anne can have access to his phone at any time. “Sharing custody of my partner’s child is difficult, mainly because contact with his mother can trigger memories of the affair,” she says. “But I also want the boy to grow up with both parents, so it’s a compromise I have to make. I took Patrick back because I love him – you can’t just turn that off. The main thing is that we continue with total honesty.”

Patrick had thought he might never win back her trust. “There’s no excuse for my cheating,” he says. “The time we spent apart was some of the worst in my life. So I had to really commit to her; I apologised a thousand times and meant it and I have to stick to her rules of being totally honest and only having a very practical relationship with the mother of my child.”

Facebook Twitter Pinterest One reader discovered his wife had debts on five credit cards and had recently been made redundant. (Picture posed by models.) Photograph: katleho Seisa/Getty Images

Tibbitts says communication is key. “You have to let the anger, hurt and frustration out: only then can the betrayer begin to learn from their mistakes, be forgiven and forgive themselves for their actions,” she says.

Of course, infidelity is not the only way a partner can let you down. When the Guardian asked readers about relationships that had survived betrayal, Lara told us how her husband had applied for a job abroad without telling the family. Paul, meanwhile, revealed how, after more than a decade of marriage, he found out that his wife had amassed secret debts of more than £40,000. “It came to light only two weeks ago,” he says. “We were walking the dog, and I asked Claire to transfer some money into my account to put into savings. She suddenly looked very embarrassed and said she was overdrawn.” He discovered she had debts on five credit cards and no way to pay them off, as she had recently been made redundant. “I’m due to retire soon and receive a lump sum,” he says, “and now I’m going to have to spend all of it paying off these debts.”

Paul, 66, is adamant that he wants to stay with Claire, however. “Our trust is damaged and I definitely felt cheated, but of course I still love her and we’re going to stay together. We’ll tackle these debts as a couple – that’s what being in a real partnership is about.” For the therapist Cristina Vrech, age can be a factor in couples’ decisions to stay together. “In my experience,” she says, “older couples might be more committed to staying together because they are aware of the work that needs to be put into a relationship for it to function.”

However old you are, Tibbitts says the only way to move past a betrayal is through the “three Rs”: responsibility (someone has to accept it), remorse (someone has to feel it) and, of course, reconciliation. “Time isn’t a healer when it comes to betrayal,” she says. “Without actively addressing the problems in your relationship, those old betrayals can still be brought up and triggered, no matter how much time has passed.”

If Paul and his wife are to stay together, Tibbitts says, “she must continue to be honest about what she has done. If there are more revelations, the relationship may not cope. She also has to present a real sense of remorse for a recovery to happen and for him to believe it won’t happen again.” Paul now has access to his wife’s accounts, in an effort to maintain honesty, but closure remains some way off. “That is a long process,” Tibbitts says. “Both parties have to want to heal the relationship and going to therapy can provide that space.” Paul is keen to avoid the therapist’s room, though, saying that once the debts are paid off “things will go back to normal”.

Facebook Twitter Pinterest ‘I wouldn’t encourage people to stay together for the sake of their children or just to keep the peace,’ says therapist Maggie Morrow. (Picture posed by models.) Photograph: skynesher/Getty Images

Staying together is not always the best solution, of course. “Sometimes the best closure is separation,” says the therapist Maggie Morrow. “I wouldn’t encourage people to stay together for the sake of their children or just to keep the peace. There’s so much potential to be explored in a relationship, but unless you’re both committed to that, you’re better off being cordial apart.”

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Tim, 50, remembers: “My ex-wife had three affairs in our 20 years together. After each affair, she would beg for forgiveness and I foolishly believed her.” With the couple sharing children and a business, he felt a split would be too damaging. Yet after the third affair, he reached breaking point. “We never worked on the underlying issues that led to these affairs, and so separating was the best thing we could have done. Now we have a much better relationship apart – we’ve even remained business partners, which has been difficult, but works well.”

By contrast, 25-year-old Sienna was determined to work things out after her boyfriend two-timed her four years ago. “We were young and went into our relationship with some naivety,” she says. “So when he cheated on me during his time studying abroad, I was devastated.” But he “begged, grovelled and promised” never to cheat again – accepting responsibility and showing remorse – and both of them “speak much more openly now about whether we’re feeling attracted to other people or finding our relationship stagnant”. Since their reconciliation, Sienna has had the best years of her life, she says. “We have a strength that we didn’t have before. It’s so easy to judge other people’s relationships but I wish we could change our preconceptions that unfaithfulness is something not to be forgiven.”

Ultimately, Vrech sees Sienna’s experience as an ideal example of how to deal with a betrayal. “When a betrayal happens, the relationship as it is known is over,” she says, “but within this ending there is the space for a new beginning. I’ve seen many couples overcome betrayal and then look back and say that, while it was a difficult experience, it made them a better couple.”

Names and other identifying details have been changed