'If he or she cheated on me that would be it - over'. Adultery is so tacky, young couples tell Emma Cook, nothing less than perfect loyalty will do...
JULIE, 29, and a production manager for a television company, has extremely high hopes of her current relationship. At the merest mention of infidelity, she's visibly appalled. "I would never, ever put up with it. If you want maximum happiness and enjoyment in a relationship, you need trust. That means being faithful. I want emotional satisfaction. Perhaps I am demanding but I don't see why I should compromise." And who can blame her?

After one semi-serious relationship that ended unsatisfactorily, she wants this one to work. She met her current boyfriend last summer and now they're talking about moving in with each other. "In a way I have to think that my relationship is the best and we're both going to make each other happy. If we've both got such high ideals we'll make more effort to work harder at it." Her friend Michelle, 26, agrees."You see all these middle-aged women in the news, like Hillary Clinton and Robin Cook's wife, and you just feel so sorry for them. I can't think of anything more humiliating - especially if they decide to 'Stand by their man'. It just seems such a compromise. Why do they put up with it?"

Julie and Michelle echo the thoughts and feelings of many young women - and men - considering marriage or co-habitation and deciding exactly what value they place on them in their lives. According to a survey published in the Daily Mail last week, more people than ever believe that it is wrong to have an affair, even if no-one gets hurt. Interestingly, younger people are more likely to feel this way than their older peers.

The Mail made much of the fact that the figures showed how women are "turning against marriage". They point to the under-35 sample, where "only" 68 per cent of them appear to want to marry, compared with 75 per cent of men. Certainly more women are realising that they don't need marriage to lead a financially secure life. Just as men are also realising that they can't rely on marriage as a domestic convenience; that sort of contract between the sexes exists less and less.

The picture that emerges from the men and women I spoke to is that both sexes want to believe passionately honest and committed relationships can exist. But they're not prepared to compromise like older generations because they can quite literally afford not to. That doesn't mean they're rejecting the institution of marriage. On the contrary, both sexes appear to idealise the whole package like never before. Paradoxically, the yearning for a rose-tinted, perfect marriage increases alongside the actual levels of infidelity: the Mori survey found that almost a third of divorcees cited infidelity as the reason for breakdown in marriage, even though 81 per cent of respondents believed it was wrong to have an extra-marital affair - four per cent more than in 1991.

It is even more marked among the 25 to 34-year-olds, where 78 per cent feel it's wrong, compared with 69 per cent of 45 to 54-year-olds. One explanation is that so many young people have grown up with divorce - one in three under-25s - that the experiences of their parents has made them more puritanical.

Paul, 27, is a graphic designer living in London. His parents divorced when he was 10 years old and he's always been determined not to repeat the pattern. "I'd be absolutely horrified if I discovered my girlfriend was being unfaithful. That would be it - I'd end the relationship immediately," he says. "I know the unhappiness it can cause. The person is basically saying, you're all right as the bread-and-butter in a relationship but if something catches my eye, I'll go for it. It shows you're not valued enough and it's insulting. They always say men are more likely to be unfaithful but among my friends, men are more paranoid about it happening to them than the women."

Other men I spoke to who had avoided monogamy in their early twenties appear to have shifted their views since they've been in a relationship they truly value. Ben, 31 and a publisher, says, "I know my girlfriend would be devastated if I was unfaithful so to a certain extent I've changed my ways to stop hurting someone else. It's about knowing someone else is emotionally committed to you." That never used to stop him in the past, though. "I've been in many situations where fidelity wasn't important. Now it is. I think a good relationship has three angles that need to be fulfilled; intellectual, emotional and sexual. If one or two of those isn't working, you'll wander."

But even if you do, is it really the end of the world for every relationship? Clearly young people seem to think so, although Relate spokesperson Julia Cole, in her own experience of counselling, disagrees. "Marriages do survive infidelity. I would say it's about a 60-40 ratio of couples who stay together."

Denise Knowles, also a Relate counsellor, adds, "So many people say they couldn't handle it if it happened to them. But when it does, a lot of people find they don't want to lose their partners; that there was obviously something not quite right and they want to work it out." Knowles says that facing up to an infidelity and exploring the cause can strengthen a partnership. "A lot of people who sort through an affair find their marriage is a lot more honest. You have to accept the original relationship has ended but instead you can develop something new and it tends to be stronger."

When Melissa, 33 and an advertising executive, discovered her partner had been seeing an old girlfriend her initial impulse was to finish the relationship. Since her boyfriend came clean about the affair and suggested they should see a counsellor for both their sakes, Melissa decided to give him a second chance.

"It really was the first time we had both sat down and discussed how we felt," she says. "As a result, I feel I can confront him about any emotional issue and we're much closer. Perhaps it took something like that to shift us out of the rut we were in. Five years ago I'd have said, what a compromise. Now I think there are worse things that could happen to a couple - like falling out of love with each other."

If the younger generation sniff at those women and men who do forgive their partner's misdemeanours, it's partly because their ideals have never been put to the test. Dr Janet Reibstein, psychologist and co-author of Sexual Arrangements: Marriage, Monogamy and Infidelity, says, "All our past studies showed this: the younger you are, the more idealistic your beliefs. They haven't experienced the complexities of marriage, of having affairs and getting back together." This is compounded by raised expectations in general. Since marriage is no longer an essential social and economic contract, it's increasingly viewed as a uniquely special relationship. Reibstein says,"It has to be perfect, with everything packed into it. That's what we ascribe some of the cause of the rise in affairs to. If it fails on one front, it felt like a total failing." She says that partners then feel so disillusioned they are more likely to start an affair.

The only way of breaking such a vicious circle is, it seems, to set out with more realistic expectations in the first place. Janet Reibstein advises: "The strongest message is to be more gentle with this institution. The important thing is to try to recognise the fallibility of the two people in it."