Perel’s approach is different. Not only does she get her clients talking about sex, ever mindful of the relevance of sexual desire in relationships, but she also sees infidelity as a complicated business that often lacks a clear villain or victim. “Betrayal comes in many forms,” she says. “You can be the person who has steadfastly refused your partner for decades, but then he cheats on you and you’re the victim? The victim of the marriage is not always the victim of the affair.”

Instead of treating an affair like a traumatic wound one partner shamefully inflicts on the other, Perel gets people to talk about why they strayed. “Before I tell a person you have to stop, I want to know: What is it for you? How mesmerised are you? Who are you in your affair?” Rather than punish people for their selfishness, their shortcomings, their lack of self-control, Perel wants to know what made them do it, what they were looking for, and why they felt they needed to stray to find it. “The debate is that once you make it complicated you’re trying to be a moral relativist,” she says. “But working with infidelity is about working with the existential dilemmas that surround commitment and loyalty and fidelity and love.” Sometimes, she adds, if a couple can be guided to ask the right questions and listen for the answers, a crisis of infidelity can help them talk about sex and intimacy in a way that brings them closer together.

This approach has its detractors. “Infidelity is a violation. And when you do something that destroys the well-being of the other person, it’s not neutral, it’s not fair, it’s not love,” says Janis Abrahms Spring, a Connecticut-based psychologist and author of the bestseller “After the Affair”, one of the first books to label infidelity a psychological trauma. “The reason my book has been so successful is because it provided a language that captured the heart of the hurt party and made them feel less crazy and alone. For Esther or any therapist to in any way minimise that pain is to retraumatise the traumatised patient.”