Becky was born into the druggy, hedonistic chaos of the late 70s. Her mother had three more children, by three more men, and three husbands, none of them Becky's father. "My mum," Becky says, "was a bit of a nutcase." The only family philosophy ever discernible to Becky as a child was: Do not trust anyone.
"I grew up craving normality. I can remember having rows with my mother and shouting, 'I wish you were just fucking normal!' And she'd say, 'What do you mean - normal? You mean ugly? Tied to a kitchen sink?' But the one thing I always wanted was security."
Becky met Jimmy, in her early 20s: "To be honest, the main appeal was that I felt he was just normal. A caring, normal, grounded person. He was like a guardian angel." They fell in love, lived together, had a baby boy, decided to marry. Weeks before their lavish wedding, they went to Paris for a weekend. Becky woke during the night, wondered why the bed was empty, and found her fiance in the bathroom of their hotel room - having sex with a stripper.
Becky was hysterical; beside herself. The friends in whom she confided all urged her to leave him. She had a good job; she could support herself and her son. But one month later, in a Valium blur, she walked down the aisle. "But I had my really strong head on. It wasn't for me. I was very clear about it. I told Jimmy, I'm marrying you for my son. I wanted to give him security; simple as that. I wanted to have the same name as my son. And I didn't want to be like my mum."
The political debate about marriage this week was arresting, not because it spelled out how many people behave like Becky's mum - but how many, often simultaneously, share Becky's view. Marriage in the mid-70s was perceived by many as a pernicious institution; the enemy of individualist self-expression. Feminists called it legalised prostitution; communists regarded it as a capitalist industrial invention, to subdue the proletariat. Radical progressives aspired to overcome marital emotions such as jealousy altogether, not by institutionalising but transcending them.
Yet when David Cameron declared this week that strong families are at the heart of strong societies, not a single soul stood up and said he was wrong. Some on the left queried the feasibility of legislating for marital accord; others questioned the point of a £20 tax break.
So has the nuclear family really proved itself incontrovertibly superior to all alternative propositions? The benefits of marriage are indisputable, for men at least. The healthiest, happiest, richest men are all married, while single men score lower on every index of wellbeing, with one exception: money. On average, men's post-divorce income goes up by 5%, whereas women's goes down by 17%. As the overwhelming majority of divorces are initiated by women, the Tories are wasting their time and money by offering an extra £20 quid to stay married. The fact that divorce makes women poorer has not deterred them thus far.
But this brings us to the heart of all statistical investigation of marriage. "Married people are, without a doubt, getting healthier and wealthier. They score higher than any other group," acknowledges Penny Mansfield, the chief executive of One Plus One, an organisation that studies relationships. "But is that a correlation, or a causation? This is a really difficult thing to put your finger on. We'd have to do a controlled experiment with very similar people, and let one lot get married, and one lot not. And that's never going to happen.
"Because we now have the acceptance of long-term cohabitation, people who go into marriage and stay in marriage are a more homogenous group. They are people who believe in certain things that contribute to stability. So the selection effect is really important. Yes, it's true that married couples on average stay together longer than cohabiting couples. But cohabitation is such an unhelpful word, because it covers a whole ragbag of relationships, so it's not really comparable. We're better off talking about formal and informal marriages: those that have legal certificates, and those that don't. Is there any difference between a formal and informal marriage? If we really compare like with like, I'm not sure you'd see much difference."
Mansfield likens married couples to private-school pupils. Exam results at Westminster, a private school, may look superb, compared to the local sink comprehensive. Send the local comp's kids to Westminster, though, and they won't necessarily replicate those results. "Marriage doesn't guarantee successful lives."
The distinction between correlation and causation cuts to the heart of the debate about marriage. The evidence is unequivocal; children raised by married couples are healthier, do better at school, commit fewer crimes, go further in education, report higher levels of wellbeing. It is easy for politicians to deduce - and assert - that married couples therefore produce superior children. But the children do not necessarily do better because their parents are married and there is actually very little evidence that marriage alone, in the absence of anything else, benefits children.
Rising divorce rates are often blamed on the process "getting easier", but in fact it has remained unchanged for centuries. An attempt to introduce no-fault divorce in 1996 failed, so divorce lawyers remain bound by a 1973 act that requires one party to blame the other. Karen McKay, chief executive of the family lawyers organisation Resolution, put it bluntly. "It's a bit like abortion; you can't have divorce on demand. You have to cite certain specified grounds. And that can be highly inflammatory. The Daily Mail seems to have this idea that otherwise, people will go around saying 'Oh, it's Tuesday, I'll go to Sainsbury's and then I'll have an abortion, and now oh look, it's Wednesday, I think I'll divorce my husband.' But it isn't like that."
What, then, about therapy? Does that help? An experiment in 2003 showed marital experts videos of couples trying to resolve a conflict, and asked for their predictions for each relationship. The therapists' predictions proved no better than those of lay people who saw the videos. Nevertheless, counsellors and therapists remain the most effective tool in supporting marriages. A massive public investment in couples counselling might generate results, and must at least be worth a try, but in most cases, by the time a couple is desperate enough to see a counsellor, it is too late to save the relationship.
If counselling could be redefined not as an emergency measure but a mundane precaution - like an MoT for your car - it might stand a better chance. Looking back on my own marriage, which ended recently, I think that had we seen a therapist after two years, instead of five, perhaps we would still be together. Instead, in what should notionally be the prime of my professional, productive life, I exist in a semi-functional half-life of depressive disbelief and regret.
Julie married her childhood sweetheart in 1961. "I very much bought into the idea of sublimation of the woman's identity into the man's. I had this complete and utterly consuming passion about that role. And having children would be the ultimate culmination of that loving relationship. But of course, I had absolutely no idea what it was going to be like.
"It was terrible. It was looking after everyone else, and putting on a bright face when your husband came home. But you've got a wonderful husband and five gorgeous children. What are you depressed about? But I was terribly, terribly depressed, for most of the time. And medicated. The kids were coming home and I'd be crying into the coal bucket. I just didn't know where I was. I didn't understand at all. Piers [her husband] was confused too: he'd say, oh you're so complicated - and that's what I thought too - until we began to see these studies."
Slowly, the depth of housewives' depressive despair became clear to everyone. "There was this sense that women were now able to describe and analyse what was going on in marriage. After the 70s I stuck it all together and I was never depressed again.
"It didn't make me angry with Piers. It wasn't his fault, any more than it was mine." Instead, Julie encouraged her husband to go and find another romantic relationship - to ease her sense of responsibility for his happiness. "I thought of it as being individualist. I thought it might be helpful to him. The decision was probably quite adventurous, I suppose."
Piers soon found another sexual partner - a family friend. Wasn't Julie jealous? "Well, it was difficult. But I just felt that jealousy was something we should sit on or try to get rid of. It's a very destructive thing, jealousy. And here we were, institutionalising it in marriage. I didn't want that."
Did she manage to overcome it? "I don't think I ever overcame the uncomfortableness of it, no."
After 20 years of this peculiarly psycho-70s, sexual experiment, Piers left Julie for the other woman, who he has subsequently married. Julie lives alone in the family home. How does Julie look back on it now? "I look back on it as a disaster since he left. My life has been a complete tragedy." Even now, after the agonising bitterness of a failed experiment, Julie still speculates about possible alternative romantic arrangements; communal communities, perhaps, or maybe weddings deferred until one's 60s.
Becky now has four children with Jimmy, and after years of rage and resentful self-sacrifice she seems to be finding some kind of serenity. "We both work, we have children, and the roles are pretty fucking confused. He still acts as if I don't contribute to the household. Having got to know his 'normal' family, I realise they're pretty dysfunctional too. And he does make me feel that what I say or think is invalid - and I compromise far more for the sake of the marriage than he does.
"But there is a sense of security in referring to myself as his wife. This is my husband, and these are my children."
A decade ago, on the eve of my wedding, I attended a One Plus One conference, and was slightly unnerved by a research finding. Asked whether, after seven years of marriage, they would marry their spouse again, the vast majority of husbands said yes, they would. The majority of wives said no.
Seven years later and, still to my amazement, I left my husband. I asked Becky whether, knowing everything she now knows, she would marry Jimmy again? "No, to be honest, probably not." But would she ever leave? "Maybe if we didn't have children. But no, I wouldn't now. It would be such a massive sense of failure. I would feel I'd let my children down. What I'm doing is, I'm proving to my mother that it can be done."