Most affairs are rarely just about the desire to get steamy with someone else. They are far more often about people's inability to negotiate the relationship they are in. "People usually have affairs to cope with a marriage rather than end it," says Janet Reibstein.

Affairs are a hot topic at the moment. In discussing her hot new best-seller about middle age In Your Prime: Older, Wiser, Happier, on Women's Hour recently, India Knight caused a furore, when she professed "I don't have as much as a downer on affairs as lots of people do." She argued that hurtful and horrible as they are, if you have created a life together with someone, chucking the whole thing in the bin thanks to a brief, stupid indiscretion might not be the best idea and a tragic waste.

This caused outrage from my favourite sex advice columnist Suzi Godson who wrote in the Huffington Post a whole rosta of arguments showing just how damaging affairs can be. As she stresses, they're the number one reason people get divorced and are, unsurprisingly, one of the hardest things for couple to move on from. "Because feelings run so high, couple therapists view extra marital affairs as one of the most damaging relationship events and one of the most difficult problems to treat in couple therapy," Suzi Godson wrote.

So why do we have affairs - and is it ever possible for couples to move on from them?

I interviewed two experts. Janet Reibstein, a visiting professor of psychology at the University of Exeter, and author of one of the few academic studies into infidelity. co- written with Prof Martin Richards, it is called Sexual Arrangements: Marriage and Affairs. She has also written a seminal book on the secret to long- enduring happy relationships The Best Kept Secret. I also talked to veteran psychotherapist Mira Kirshenbaum, who is clinical director of the internationally renowned counselling centre The Chestnut Hill Institute, in the US. She has written two books on the subject: When good people have affairs. I love you but I don't trust you: the compete guide to restoring trust in your relationship.

Here's what they said.

Most affairs are rarely just about the desire to get steamy with someone else. They are far more often about people's inability to negotiate the relationship they are in. "People usually have affairs to cope with a marriage rather than end it," says Janet Reibstein. "They feel disappointed by a marriage and have become estranged from the person they wanted to love and honour." This isn't helped by the massive expectations we put on modern relationships - that they should deliver our soul-mate, amazing sex, intimacy and companionship all the time, just piles on the pressure and risks dissatisfaction.

Problems start when couples fail to manage their disagreements. "If couples don't catch things early, they start to feel misunderstood, neglected and unloved. Drift then sets in, and with it goes hope and effort. And finally couples will look outside the home for ways to cope," warns Reibstein who has been a therapist for 30 years. "Why people have affairs points directly to the problems they are having in their marriages," agrees Mira Kirshenbaum. "Affairs are rarely about making an exit but an attempt to deal with a desperate situation."

Here, according to the experts, are the seven most common triggers for an affair.

1. You've stopped having fun as a couple

When life gets busy with work and children, time to enjoy yourself as a couple is suddenly bottom of the list. You go to work separately where you engage in separate worlds with people your partner barely knows. Once home, your primary focus is looking after the kids. At weekends you often you tag-team who is on duty, leaving no chance to do things as a pair. There is little chance to be reminded of all the traits that attracted you to each other. Your sex-life fizzles out. With it your sense of coupledom. Then when temptation comes along, that idea that you are an unbreakable unit has gone. There feels less to lose.

Can you recover? Never forget how devastating affairs are to relationships, says Prof Reibstein. Just like a major wound, healing will take a long time and usually require outside professional help - together. As in all affairs, if you have been the unfaithful one you first need to convince your partner that the affair has really ended. You must lose all contact with your lover and the temptation they represent. Then you have to be prepared for how long it will take for your partner to heal. After the healing, for marriage to survive in the long term, you must then go back and try to fix what caused that affair to begin - in this case fact that you stopped spending quality time together. "My research found that couples who are happy and who endure all make a huge effort to make time for each other," says Prof Reibstein. "They always have a night when they go out on their own. They talk and listen to each other every day. They close the doors at night and keep their kids out of the bedroom."

2. You've become strangers living under one roof

For similar reasons that you fail to have fun as a couple, you also become mentally disengaged. You've stop sharing your inner-most thoughts with each other, stopped tuning into each other. You start to feel like two strangers sharing a house. You feel lonely in the very place you know you should feel most loved and secure. You find that arguing is the only way to get each other's attention or create the emotion and closeness you crave. Subconsciously doing something as drastic as having an affair is way to bring things to a head.

Can you recover? Even if it is a cry for help, you should never underestimate the injury caused by an affair that has been discovered. The injury to trust, the sense of betrayal, as well as the thought that someone has taken your 'place' is hard to get over, says Prof Reibstein. But if you do recover from it you need to commit to tuning into each other's thoughts and needs once more. It takes vigilance to remain close in a relationship when so much is going on around you, but for your marriage to survive long term it has to be done.

3. You can't resolve your conflicts

You don't like arguing or find it hard to vocalise your feelings, so you skirt around problems rather than confronting them together. Soon you have an entire bank of grievances that you have not aired, and start to blame your partner for everything goes wrong in your life. This makes you hard to be around, and the marriage hard to enjoy. So the resentment builds still further. As a result you can't help but be drawn towards other people who are willing to listen to you and it is easy to feel convinced that they understand you better than your own partner does. "Many people report that the greatest pleasure in an affair is finding someone whose arms are wide open to all the parts of you that your spouse seems to reject," says Kirshenbaum

Can you recover? Slowly you need to work through all the causes of your resentment with your partner. And be prepared to hear about their resentment towards you. To work this out successfully it's essential to do it with a professional, says Kirshenbaum. "Talking things out" without a wise referee too often turns into a knock-down, drag-out fight." Then you have to work out ways to help you both approach conflict more openly and quickly in the future.

4. Someone else was just there

It is depressing but true: Opportunity is one of the most common triggers for an affair. You run in to a colleague after a meeting. Or find yourselves alone together at the bar in a faraway hotel on a business trip. You get talking to a fellow parent at the school gates and decide to grab a coffee. You have dinner with an old flame who's asking you for advice. You don't plot it, but before you know it is happening. "A little bit of discontent and a little bit of attraction is very often all it takes to set reckless passion ablaze," says Kirshenbaum. "Then you find you're in an affair you never wanted and never sought out. But it soon takes on a life of its own, and you don't know what to do." Opportunity explains why the number women having affairs dramatically increased after the 1970s when they joined the workforce and had more control over their time, says Prof Reibstein. And she warns, watch out most for those co-workers. "You see them every day, you get close to them, and they make you feel better about the things that don't feel good in your relationship."

Can you recover? Saying "It just happened" is hardly reassuring. You're trying to prove that although you were over-come by the circumstances you'll never do it again, so rebuilding trust here is the key, says Kirshenbaum. Show them that you realize how deeply and painfully hurt they've been. Recognize that it was your choice and your responsibility for making it--things don't 'just happen' and affairs are a series of steps taken - or not. If they believe that you understand the damage you've caused, slowly after a long period of healing they might come to believe that you'll never want to hurt them like that again.

5. You want to feel alive again

You feel bored, like your life is stagnating, that your relationship is not giving you what you want. So you start looking for ways to feel excited and renewed. Few things are less boring than the first throws of an affair. The passion crammed into a furtive meeting. The struggle to meet in secret. The efforts to keep it all hidden. The jeopardy. The wild hopes. All this makes an affair intoxicating compared to the routine of a marriage where even sex and fights are all too predictable, says Kirshenbaum. But be warned, affairs too easily turn into a horrible mixture of boredom and stress.

Can you recover? If a sense of stagnation drove you into the affair, you're going to have to face what has caused this in your marriage. And true, doing the same things over and over with the same person can inevitably feel stagnant. But a continual effort to shake things up, to look for new things to do and new ways to do old things, will pay huge dividends.

6. You can't help wondering who else is out there

A marriage is supposed to last a lifetime, but if you are feeling unappreciated and misunderstood you are more likely to start wondering who else is out there, says Prof Reibstein. That's especially true when so many other people look so good on the surface, so you dip your toe in, and before you know it you're dipping in a lot more. But be warned, despite the initial passion and excitement, often affair sex isn't as satisfying sexually as the sex is within a long-term relationship, where you know each other well and have learned how to please each other. Often relationship sex feels boring only because couples fallen into the pattern of doing the same old thing.

Can you recover? "I've seen it happen over and over where someone had an affair, came to realize that the grass was not greener on the other side, and that one's partner is really was a pretty good deal after all," says Kirshenbaum. But if this kind of affair is found out, stressing what an idiot you have been is a start. But you'll also both need to work out together what was causing the marriage to feel lacking and how to get it kick-started again.

7. You married the wrong person

You once prided yourself that your family would always come first and that you would never have an affair. But as the years have gone by, you and your partner find you have less and less in common. Your partner is someone you think you should love, rather than someone that you do. When you meet someone else you all this suddenly becomes clear to you and you fall head over heals. This amazing sensation may be simply the product of prolonged misery in a marriage, but it also could develop into genuine love. Those still wedded to the idea of their "perfect" family may lead a double life for years. More often their new partner or desire for happiness will force them to make an exit.

Can you recover? Your original relationship may not recover-- and certainly won't if you don't want it to, says Prof Reibstein. If that is so, the most important thing is to try to minimize the hurt, so you can both move forward to have successful relationships with other people that are not bogged down with bitterness and mistrust.

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