Modern life presents us with numerous ways to cheat: texts, direct messages, or plain old-fashioned affairs. But is infidelity really betrayal? Radical couples therapist Esther Perel reveals why it might be exactly what your relationship needs

Photograph: Phillip Toledano

Is anyone monogamous any more? Truly monogamous? We may not be having serial affairs in the John Terry/Tiger Woods mode. We may not find ourselves transgressing as dramatically as Iris Robinson. Or as publicly – and ineptly – as Ashley Cole. But we are probably less monogamous than we used to be, aren't we? We're perhaps having extended flirtations; serious and not-so-serious dalliances; special, ostensibly platonic lunch dates with people we see more regularly than we'd like our partners to know. We are, at the very least, testing the borders of fidelity via the medium of text message, or Facebook connections, or Twitter exchanges; the Vernon Kays of the non-celebrity sphere. And some of us are having fully fledged, old-fashioned, impassioned affairs.

Ask around and you'll see. I asked: friends, friends of friends of friends, online contacts and distant colleagues. I asked some youngsters, some older people, some women, some men. I asked them about the grey areas of their connections with people who were not their partners; I asked what qualified as flirtation and what crossed the line. I asked them how often their extended flirtations became affairs. I asked those who were having affairs how they had them. (I changed their names; sometimes I switched genders. Many of the stories are secondhand – one of them could be one of yours. Or one of mine.)

Joe is not sure if the iChats he exchanges with his colleague Maggie qualify as merely flirtatious or as something more charged, less moral, potentially dangerous. He wouldn't want his girlfriend, Isabel, to know about them, obviously. But does that make him an adulterer-in-waiting? Does the iChat exchange make Joe less faithful to Isabel than he used to be?

Claire thinks she could be on the verge of cheating on her husband, Mike, with Al, a man she re-met on Facebook three months ago. Al and Claire were friends at university; there was always an attraction there, although they never acted on it. Ten years after graduation, at the precise point at which Claire and Mike decided to start trying to get pregnant, Al got in touch, and he and Claire began emailing regularly. Those messages have become increasingly suggestive; Claire's now wondering whether to do as Al wants and meet for a drink.

Tony sent his ex-girlfriend Tracey a direct message when he found her on Twitter, telling her that he hadn't stopped thinking about her in the seven years since they split. Tracey direct-messaged him back several times; she hasn't yet told him she's pregnant with her first child. She's not sure she wants to.

Nic doesn't think kissing counts as cheating, especially if both parties are in a relationship ("Equal power!") and a bit drunk; and Steph says it doesn't count if it's with a celebrity.

Chris wants to leave his long-term girlfriend for the woman he met before Christmas – the woman he's since begun to think of as the true love of his life. They haven't had sex because they've agreed that having an affair is not a stable way to begin a new and committed relationship. "Because it isn't an affair," says Chris. "It's just that we're in love."

Graham recently downgraded his extra-marital affair from a physical relationship to an intensely emotional engagement conducted entirely by text. He thinks that's best for his marriage. Elizabeth, on the other hand, is delighted to discover that a very physical affair with a younger man has cheered her up so much that she finds herself being much nicer to her boyfriend and children. "I had the perfect affair," she likes to tell close friends. It was so much better than the one she had three years ago.

And Michael is actively looking for a mistress. "I am recruiting," he says. He has no intention of leaving his wife. He doesn't want to try dating sites designed for people seeking illicit affairs; some of his friends have done just that, but Michael thinks they're for amateurs. He wants "to do it the old-fashioned way…"

THere are few reliable statistics relating to rates of infidelity. It's not the kind of thing people tell the truth about, or have ever told the truth about. Psychologists think men traditionally overstate their infidelities, while women understate. The most regularly invoked figures suggest that roughly 30-40% of those in a marriage or long-term relationship will be somewhat unfaithful at some point. Couples counsellor Andrew G Marshall, author of How Can I Ever Trust You Again? Infidelity: From Discovery to Recovery in Seven Steps says he's seeing more of it in his practice. (Although he adds: "That may be because I'm looking for it. And it may be because all the technology that makes it easier to cheat also makes it easier to get found out.") Relate's Denise Knowles says she's treating more people as a consequence of affairs, too.

Logic would suggest we're having more affairs than ever. We're presented with more opportunities to cheat. We work more and travel more, and consequently are more absent from our homes. The evolving landscape of technology means we are connected – sometimes intensely and continuously – with many more people than before. Technology also means that the very definitions of infidelity have broadened. Emotional infidelities are increasingly an issue; entire affairs are played out online; intense relationships – which may or may not blur the line on friendship, who knows? – flourish via the intimacy of the text message exchange.

And yet we're still incredibly reverent about, and attached to, the ideal of monogamy. Both the major political parties are attempting to enshrine monogamy in pro-family policy; both made monogamy a cornerstone of their election campaigns. En masse we are critical of other people and their infidelities. We're fantastically sanctimonious regarding celebrity transgressions. We were glad that John Terry was stripped of his captaincy; delighted that Tiger Woods lost his endorsement deals as a consequence of his alleged infidelities; overjoyed that Cheryl gave Ashley the boot. We condemn the unfaithful publicly and gossip about them privately. We condemn ourselves when we transgress; we lose ourselves to guilt and suffer identity crises: how could we do this? This isn't who we are!

Why are we living this dichotomy? Why do we support the idea of monogamy so heartily while not managing to be monogamous? Why do we persist in having affairs, persist in believing in monogamy, when we're not comfortable with or especially capable of either?

Esther Perel thinks she knows. She's a New York-based couples therapist; a Belgian-accented, 52-year-old minx of a shrink. She's a self-styled "voice on erotic intelligence… a sexologist", and she peddles what is possibly the most insightful, revelatory and controversial line on sex and love and marriage of our times.

I first met her three years ago in her offices – a suite of rooms on Fifth Avenue right next to New York's Museum of Sex – to discuss Mating in Captivity: Sex, Lies and Domestic Bliss, the book she'd just published about sex in long-term relationships. Then, her main point was that eroticism comes not from closeness, not from intimacy, but from precisely the opposite. From distance, from moments of jealousy, from a constant awareness that you do not own your partner no matter how long you've been together; that other people fancy them, that they always have the potential to sleep with someone else. I remember at the time being both genuinely shocked by her thinking and completely poleaxed by how right it seemed. It was instantly familiar. It resonated like the chorus of an incredibly good pop song.

Perel's newest obsession is infidelity. She began writing about and considering it in earnest as far back as 2002; after the 2007 publication of Mating in Captivity she discovered that faithless love was all anyone really wanted to talk about, and demand for her unique perspective escalated. She's been chairing workshops on it and speaking at conferences about it ever since. Perel began refining her ideas on affairs and monogamy, and concluded that pervading notions and received wisdom on both are unhelpful, outdated, reductive and ineffectual. Perel believes that if we can revisit our ideas on infidelity, start properly understanding why we do it, become more tolerant of the fact that we do it, then we're in with a better chance of maintaining a happy marriage.

When I interview her via Skype (which is how, she says, she spends half her life these days. "I even see patients like it. We will get very intimate, just you wait and see!"), I ask her: why are we all so obsessed with affairs?

"Because it's important!" she says. (Perel, who was an actor before she became a psychotherapist, is not afraid of ramping up the impact of her discourse with high drama.) "I don't think there is another facet in relationships that can illicit so much fear, gossip and fascination. It tops them all."

Infidelity, she says, is one of the great recurring themes of the human experience. "And we are not monogamous! We are not! Monogamy is human, but human beings are not monogamous! By nature! Historically we have always been unfaithful – and always condemned infidelity. For a glimmer of passion, or whatever, people have been willing to risk everything. Women more so than men."

Really? Female infidelity is a riskier business than male infidelity?

"Of course! Still, today, there are eight countries where women can be killed for being unfaithful. And before, there was no contraception! Everything about female sexuality was more dangerous. Rates of female infidelity have grown enormously, in accordance with women's economic independence. In Latin American countries it's a social phenomenon. When I went to Argentina all they wanted to talk about was female infidelity. It's [a marker of] acute social change. It's not just a few women. It really toppled the traditional male privilege. What does it mean when this happens in a society where it was never accepted, where men were allowed to roam around but women never could? When women begin to do what was traditionally a privilege of men, what does it do? It does everything! It changes the dynamic of power!"

So infidelity might be considered an important indicator of social evolution?

"Definitely. You can always use infidelity to track social changes. And yes, female infidelity is a statement of female empowerment; but then again, infidelity is a statement of empowerment for anyone who practises it. It is a rebellion."

This is what Esther Perel does. She re-spins affairs, throws new light on them, offers completely new perspectives. She can make affairs seem positive: "I have a client who says it is a facelift and antidepressant in one – but much cheaper!" She can make them seem inevitable, the consequence of our intense, heightened, essentially unrealistic expectations of romantic love: "The men and women I work with invest more in love and happiness than ever before, yet in a cruel twist of fate it is this very model of love and sex that's behind the exponential rise of infidelity and divorce. Fascination and disillusion stare at each other."

She can transform the revelation of infidelity into the catalyst for the rebirth of a relationship: "The standard ideas that affairs deplete intimacy, that affairs deplete the marriage, they are always harmful – I say: this is one possibility. But there are others. Affairs also are enormously enlivening. Re-eroticising. They balance the marriage. People who have affairs don't always want to leave the marriage. Sometimes, often, they are looking for a way to stay!"

And perhaps most surprisingly, most controversially, she takes the traditional cliche of the faithless man or woman and refashions it: "When you have an affair, this is rebellion! This is not a mild act! We have affairs to beat back the sense of deadness. We have affairs not because we are looking for another person, but because we are looking for another version of ourselves. It's not our partner we seek to leave with the affair, it's ourselves. It's what I've become that I don't like. It's how I've truncated myself. That there are parts of me that I have been so out of touch with, for decades… And of course, we live twice as long. We are different with different people."

Whatever else, Perel says, we do not have affairs simply because we are bad by nature; or deceptive, or selfish, or cruel. "It's not just about right, and wrong, and moral. Particularly in America and in the UK, this is what we say about affairs. It's wrong. We talk about cheater. Philanderer. Liar. Narcissist. If it's not all those condemning words, then it goes to pathology. Borderline personality disorder. Childhood trauma. Addiction. We hide behind moral condemnation, or pathologising. This is not helpful, and not true. If it is true, then there are a lot of us suffering with childhood trauma and borderline personality disorders, and we have been suffering from them throughout history! We need to start to understand infidelity in terms of the complexities of life today. We need to think in terms of the failed ambitions of love."

Esther Perel is an impassioned, intoxicating speaker. She talks fast and hard and she weaves her clients into her monologue. She references them constantly: anonymously, brilliantly, luridly, with compassion and as excellent, gossipy snippets. They are her characters, and her living proof that her theories have merit. Sometimes, as she's telling me their stories, I get goosebumps. Sometimes I feel a bit teary. Sometimes it's as if Perel's talking to me – about me – and no one has ever understood me quite as well.

At other times, Perel loses me altogether.

I'm on nodding terms with the misery infidelity causes. I've seen it, lived it (from both, equally grim, perspectives), and propped up close friends who were suffering because of it. I am not sure if this misery comes from those artificial social constraints, from the kind of ill-advised, fiercely held false ideas about relationships that Perel hopes to debunk; or if it just really, really hurts when someone we love sleeps with someone else. However we learn to think about it, won't that always be the case? Won't it always just really hurt?

Perel says she doesn't want to diminish the trauma of infidelity. She invokes her clients again, recalls how "destroyed, completely destroyed" a male patient she had seen only that week was by the revelation of his wife's affair. She says that in the aftermath of an affair, both people are in crisis ("Yes, it is a crisis of two people. Not just of the person who was cheated upon") and that she wouldn't expect anything else. "At that point it is my role to contain them, to give them structure, to slow them down. And to say: 'You can't decide the future of your marriage on the heels of the revelation of an affair.' Because in that first stage, with the whole turmoil, the tendency in the condemning society is to say: 'Leave!' I'm saying: 'This is the one moment when you should not leave.'"

I can engage with the idea that a more tolerant view of the person who has committed the infidelity could be helpful in many ways. I can see that it might even help the person who was cheated upon – it could make them feel less stigmatised, not quite so much of a cuckolded cliche, couldn't it? I can also imagine that if the pressure to leave a relationship the moment an affair is uncovered were removed, some of the blind panic that currently surrounds infidelity might be diffused – because yes, affairs are much more disruptive when they precipitate the end of a relationship. And, long term, if we could abandon truisms like "once a cheater, always a cheater", a relationship that's endured an affair would have a better chance of surviving.

Perel says: "After the affair has been discovered, what needs to happen is we have to find a way to integrate the story of the affair into the story of the marriage." To ensure, in other words, that the marriage is not defined by the affair, but that it becomes part of its continuum.

I can – I do – accept these ideas. But still, even as I subscribe to Perel's thoughts, even while I am convinced that her ideas are brave, wise, smart and certainly worth pursuing, I also have moments where I struggle to see beyond the pain and unhappiness even a notional infidelity entails. Moments when I wonder if all we are doing here is seeking to excuse shoddy behaviour.

What does Esther Perel hope to achieve? Simply, she says: "There must be a response to infidelity that is more creative than divorce." She doesn't think every relationship should and can survive an affair. Sometimes, she says, affairs are initiated as an exit strategy by the husband or wife, and so must result in a divorce or a split. But more often than not infidelity is surmountable in a relationship. Marriage counsellor Andrew G Marshall agrees with her in this respect, at least. "The most miserable couples I ever see are the couples who are trying to recover from an affair," he tells me. "But equally, the happiest couples I end up with are the couples who have recovered from an affair. Affairs make you scrutinise every element of your relationship, more so than any other issue. And so if you do survive them, you will be stronger and happier as a result than you ever were before."

Perel adds: "Less innocent, perhaps. But stronger, more powerful, more connected."

Perel thinks we have to work toward renegotiating our ideas of monogamy. We need to see it as an exclusive emotional commitment, but not an arrangement that necessarily denotes sexual exclusivity. She thinks that, in time, we'll come to accept affairs in the same way that we've come to accept premarital sex and homosexuality: not as deviancies, weaknesses or sin, but as part of who we are and how we love.

How, I ask, is this different from the somewhat annoying, ultimately discarded vision of free love propagated in the 60s.

"Free love didn't believe in the old model. Free love wanted to throw the old model out. Free love saw it as reactionary, as constraining, bourgeois. The new model is an attempt to reconcile our needs for commitment and our need for freedom. Our needs as part of an individualistic society, which talks about individual fulfilment and personal happiness and more is better, and our need for secure attachment and a stable family." She points out that, while we often talk critically about the idea of "having our cake and eating it" with reference to affairs, in every other aspect of our lives – in work, in our homes, in our social lives, in our experiences of the world, in our constant quest to improve ourselves and our quality of life – we are encouraged to have as much as we possibly can of everything.

OK: but what about jealousy?

"Aha!" Perel says, and she laughs. She begins telling me about a man, a patient who, after 30 years of marriage, discovered that his wife was having an affair; after the initial meltdown, the couple decided that while they very much wanted to stay together, they also wanted to try having sexual relationships with other people. His wife has since begun to feel jealous when her husband goes away on business trips. "And, of course, the view is that jealousy is a negative emotion, it's a primitive emotion. But I said to her: aren't you happy that you feel jealous? In truth it says that you care for him again, despite the affair you had. Jealousy goes hand in hand with passion. Is jealousy intrinsic to love? Yes! It's an indicator. If you cheat on me, am I just pissed because it's a sloppy thing to do? Or am I jealous, jealous that you had with someone else what I want to have with you, or what we used to have that was special? Because that's a very different thing! I don't know that you can have romantic love that doesn't involve jealousy. The question is: how much? And what do you do with it?"

And Perel's got me onside again. If I find her version of future monogamy challenging and a little bit odd, I think she is right about the role jealousy plays – the role it should play – in our long-term relationships.

We talk a little about the new, shadowy areas of human relations: the texts and email and iChats that may or may not qualify as cheating. Perel thinks that a flirty text message exchange can be as potent an infidelity as a fully fledged, physical affair. "So you don't touch? Sometimes this can be far more erotic than sex – because it all works in your imagination." Furthermore, this rapidly expanding field of infidelity is yet another reason for us to redefine monogamy. "Do we have to put monogamy on a spectrum? Do we need to think: what does monogamy mean to me? Does it mean no sex with other people? Does it mean not to look at other people? Does it mean not to fantasise about other people? Does it mean not to Facebook your exes? Not to text your friends? Where is the line going to be drawn? Monogamy today is no longer going to be assumed. It's going to have to be negotiated."

Perel's ideas on infidelity are infinitely more useful than anything else currently doing the rounds. They would, at the very least, shake up lazy wisdom on what it means to cheat and be cheated upon. They would provoke debate, move things on. I think they should be given clinical currency. Perel's beginning to construct a book around them, and I hope she finishes it soon.

Before shutting down our Skype connection, Esther Perel says this: "At all four corners of the world, at this very moment, someone is either cheating, or contemplating cheating, or listening to the stories of someone else who is cheating, envious of that person who is in the throes of an affair – or maybe they are the lover in the affair… With every marriage, with every relationship, comes the possibility of an affair. It always will."

She's right. She's absolutely right. And we have to find a way to live with that.