Have you and your partner agreed on an open relationship or do you expect 100 per cent monogamy? she

“Have you and your partner agreed on an open relationship, or do you expect 100 per cent monogamy?” she says. In her clinical sample, “men who engaged in primarily sexual affairs were as satisfied with their marriages as non-involved men. But women in any extramarital involvement were less happy in their marriages than non-involved women”. Perhaps, she concludes, this is because men are more likely to have an affair due to sexual attraction, while women often look for emotional connection.So what can you do if you find yourself unable to resist the temptation of a fling? Or if you think your partner might have a roving eye, no matter how strong his commitment to you? Martin-Sperry advises keeping a constant check on your own expectations and your partner’s. “Men are opportunistic, if there is availability,” Dr Egan says. “Women tend to stray more when unhappy, perhaps in reaction to personal distress in their lives.”Certainly, a breakdown in marital relations is one of the distressing situations behind many affairs Glass’s research had similar findings.

He concluded that men who tend to cheat are sociable and outgoing, while unfaithful women are often needy and withdrawn. “[These are] people who have some level of narcissism, who may be selfish or need a lot of attention, or those who had a difficult relationship with their parents, particularly their mother,” says psychosexual therapist Carol Martin-Sperry.But when Dr Vincent Egan, of Glasgow Caledonian University, studied the personality traits of men and women who are unfaithful, he found extreme differences between the two. While the men who cheated scored high on the social dominance scale, the women who cheated scored low. The quest for extramarital excitement can be an attempt to “fix”an internal problem, such as boredom, low self-esteem or existential angst. Those more likely to seek an affair include “Type T”, or thrill-seeking personalities – those who suffer addictions to sex or love, and people whose egos need constant attention.

In order to give in to attraction, you have to convince yourself your relationship isn’t working, or your partner doesn’t appreciate you We give ourselves permission. And once our excuses are verbalised to a friend or the other party, they take on a life of their own.Many unfaithful people also have personalities that need reassurance or affirmation. “In affairs, people are as likely to engage in self-deception as in deception of their partners,” says Glass. Nobody wants to believe they are capable of the deception and destruction of an affair, so we create an alternate reality. People who are unfaithful are more able to rationalise and compartmentalise their behaviour. In the moment of attraction, we are fully alive to the possibilities of potential intimacy.” For Glass, what separated the faithful from the unfaithful was a set of personality traits and values.Among these values is our sense of commitment – whether that be attachment to a particular partner, or to the principle of monogamy – and how strong it is. “Attraction is a dependable constant in our lives,” she writes “It doesn’t matter whether we are happily married.

In fact, in a recent study of more than 2,000 women across the US, researcher Carole Ellison found that 13 per cent of women who had been unfaithful had engaged in five or more affairs, and most of these women had grown up with a parent who had also been unfaithful.The “I couldn’t stop myself” theory of sleeping around has some scientific gravitas then, but surely not all children of philanderers are destined to repeat their mistakes? In her influential book on infidelity, Not “Just Friends”: Rebuilding Trust and Recovering Your Sanity After Infidelity (£8.24 from www.amazon.co.uk), Dr Shirley Glass claims some of us find it easier to control unfaithful urges than others. Her views are echoed by Dr Susan Marchant-Haycox, a psychology lecturer at Birkbeck College, London. “If a child continually sees a parent being unfaithful, it could reinforce that infidelity is acceptable. As a result, the individual is eventually unfaithful to his or her partner,” she says.