I would imagine few people would ever admit that they could stand the idea of their partner being unfaithful. One woman, describing her husband's infidelity to me, said: "It was as if he has completely shattered a beautiful crystal bowl, a bowl of trust between us. There was no way it could be mended, it had split into so many millions of shards."
It seems that most women when faced with infidelity feel the same. Yesterday, after initially vowing to stand by Ralph Fiennes, her boyfriend of 11 years, Francesca Annis announced they would be splitting in the face of his infidelity with a Romanian singer, Cornelia Crisan. To add to Francesca's misery, the newspapers reported that Cornelia possibly isn't the first, either. There have been, they say, a "string of women" in the actor's past.
So would Francesca ever have been able to make her relationship work after such a betrayal? To accept this kind of behaviour from her young lover 19 years her junior, she would have to twist her head and her heart, and resist the over-whelming temptation to jump up and down, chop all his suits into shreds and change the lock on the door? But forgiving an affair isn't just about being a sad old doormat, desperate to cling on to a lover and therefore being prepared to forgive everything. Some women tend to even still see relationships in old-fashioned Parisian terms - chaps have affairs, women turn a blind eye.
One reason, I'm sure, that some relationships in which men have affairs can work, is because men and women have slightly different attitudes. Research recently showed that men find their partners having affairs far, far more difficult to cope with than vice versa. It seems that women might forgive a partner's purely sexual affair, but would find it intolerable if their bloke actually fell in love with another woman even if he didn't lay a finger on her. Physical infidelity means less to them than emotional infidelity.
And while women in this situation may not like their men going off with other women now and again, they can just tolerate it, because they know that to make a fuss about it would mean the marriage breaking up, and that, they feel, would be intolerable.
Usually, infidelity arises when there is something dreadfully wrong with a relationship that neither party can bear to talk about with the other - in other words, infidelity is a symptom of trouble, not a cause. That's why in some cases, when an affair comes out into the open, a couple may suddenly become far more honest with each other and their relationship can actually become stronger as a result.
But sometimes it doesn't work like this. Sometimes it's simply a matter of two people who love each other being sexually incompatible. Usually one person wants masses of sex and the other doesn't want much at all. But rather than break up, which would be agony for both of them, how much more sensible it is for a woman to allow a man to get his sexual needs taken care of by other women. In this case, the affairs can be the life-savers of the relationship rather than destructive bombs.
Speaking personally, I don't think I could cope with infidelity, but I do know of couples who seem to hang on in there with everyone having affairs all round. But this only works if there is complete honesty. If one partner sneaks off and has affairs behind the other's back like Ralph Fiennes did, denying it all the time, it's a terrible blow to the innocent partner when they find out. If, however, there is an agreement between them that they can each stray, as long as they always return, in the end, to each other, infidelity is no longer a betrayal at all but, rather, the result of a curious complicity between them.
The truth is that many long-term relationships are marvellously complicated things. While we all have a kind of holy grail to follow in the search for a perfect relationship - true love for ever, total honesty, absolute fidelity, shared interests and laughter - the truth is that most of us have relationships that are like weirdly knitted jerseys - full of dropped stitches, patterns all askew, too big in the arms, baggy in the front, too short in the waist.
But the point of them is simply to keep us warm, or warm enough, and if they can do that, then brilliant. And who cares what they look like to other people?
Unfaithfully yours: other expert views
OLIVER JAMES: Clinical psychologist and author of They F*** You Up: How to Survive Family Life
The number of people who accept that they are in an open relationship is very small. We each have an opinion of our sexual worth based on factors such as our appearance, social status and wealth, and we try to find people of roughly the same value as partners. If someone is with a person who they feel has a higher value, they're more likely to put up with all kinds of behaviour. Relationships are more likely to survive infidelity if the couple are married or have children together. Presumably Francesca Annis knew that Ralph Fiennes could get his hands on a lot of women, and although she looks good she also knows that she is 60, so she may have cut him more slack. But it seems even she could not cope with this.
ANNE HOOPER: Sex and relationship counsellor and author of How Was it For You?: Making Sex Much, Much Better
If relationships couldn't survive infidelity I don't think anybody would stay together. Nowadays more than 60 per cent of people have a sexual relationship outside of their marriage. A good marriage is not just about sex, it is about many other things: having a home; family; being really good friends. I don't think age makes all the difference. All men go through a midlife crisis - if you can be up-front with the problem, it can be overcome. Couples need to keep being affectionate and remember that each is the primary person for the other. And if you are going to play away, don't do it in a rude and obvious way. As long as enough love has been put in over the years, there should be enough to see them both through the crisis.
CATHERINE TOWNSEND: The Independent's sex columnist
People always say that women cheat for love and men cheat for sex - then women get blamed for not keeping their men satisfied. But I think that if someone in a relationship isn't happy, they have to bring it up - after all, my mother always said that "strong and silent equals sullen and stupid". It's easy to forget during day-to-day interactions with a long-term partner that relationships are delicate ecosystems. Cheating is often caused by communication breakdown, but it's also an act of selfishness that destroys the balance. If someone cheated once, wouldn't they do so again? A relationship can survive, but only if both parties can be honest about the reasons for the affair. The person who has been cheated on needs to forgive and move on, or resentment will build.
PHILLIP HODSON: Fellow of the British Association for Counselling and Psychotherapy
Francesca Annis' initial response to Ralph Fiennes' infidelity was clever: it didn't disrespect him and presented an explanation other than that he's tired of her. It also gave him sufficient rope with which to hang himself.I think that the wider question of whether a relationship can survive infidelity is a no-brainer: of course they can because so many do. The mistake people usually make is trying to rule a line and start again. You can't emotionally wipe the slate clean, you start again with no trust and have to rebuild it. The guilty party might say: 'It was only sex, it didn't matter, I won't do it again' but it's their future actions which will prove that. All love ends in sadness. But we can't go around avoiding attachment for fear of getting hurt.
PETA HESKELL: The Flirt Coach
Whether a relationship can survive infidelity depends on a number of factors:
1. Are they really soul mates?
2. Did they ever agree not to see other people?
3. Have they outgrown each other?
4. Was it just a drunken night out that they regretted later? Infidelity that involves an emotional connection is far more threatening. Ultimately, to survive, you have to forgive and let go. What hurts most is the feeling of broken trust. You have to begin again and discuss what you expected from the relationship, what you want for the future and commit to something that works for you both. All relationships need constant work, and if you're not prepared to do that then maybe yours is ready for the graveyard.
Additional interviews by Ele WalkerReuse content