Now, for the first time, married-couple households are a minority in both the UK and the US, outnumbered by single-person households and cohabiting couples. In the US 49 per cent of all households contain married couples. In the UK it is even fewer - 45 per cent in 2005, a drop from 54 per cent in 1996. This has caused consternation among people who believe that we could restore the primacy of marriage in modern life if we could just get couples to invest more energy in their marriages.

But the idea that a romantic partner can meet all our needs is a very recent invention. Through most of history, marriage was only one of many places where people cultivated long-term commitments. Neighbours, family and friends have been equally important sources of emotional and practical support.

Today, we expect much more intimacy and support from our partners than in the past, but much less from everyone else. This puts a huge strain on the institution of marriage. When a couple’s relationship is strong, a marriage can be more fulfilling than ever. But we often overload marriage by asking our partner to satisfy more needs than any one individual can possibly meet, and if our marriage falters, we have few emotional support systems to fall back on.

Men are especially vulnerable after divorce, because they pay less attention to maintaining social ties outside marriage. But women also fall prey to the fantasy that once they find their “soul-mate” they can retreat to an isolated island of marital bliss.

Even the best-matched couples need to find gratification and support from sources other than their partner. When they don’t, notes Joshua Coleman, a therapist and author of The Marriage Makeover, they have less to offer each other and fewer ways to replenish their relationship. Often the marriage buckles under the weight of the partners’ expectations that each will fulfill all the other’s needs.

For almost 20 years, Richard Lucas has been studying the self-reported happiness of more than 30,000 individuals. He finds that feelings of happiness increase around the time of marriage, but after a few years people return to their original happiness “set point”. People who marry and stay married are slightly happier, on average, than people who never marry, and significantly happier than most people who marry and then divorce. But such individuals already reported higher-than-average happiness before they married. They didn’t depend on marriage to make them happy - and that’s one reason why they didn’t become discontented once the honeymoon wore off. Couples who expect to find the greatest happiness from marriage are prone to the greatest disappointments.

Putting all our emotional eggs in the basket of marriage is a particular problem now that people live unmarried for longer periods of their lives than in the past. When we make romantic love our only source of commitment and obligation, we neglect the wider interpersonal ties that knit society together. This impoverishes the social lives of single and married individuals alike.

Several studies in the US reveal how couples ask love and marriage to meet too many of their interpersonal needs. Over the past two decades, according to research by three American sociologists, the percentage of people who said their spouse was a close confidante rose from 30 to 38 per cent. It’s good news that more couples are now close friends. But the flip side of this trend is more disturbing. Using US national data from 1992 to 2004, the sociologists Naomi Gerstel and Natalia Sarkisian found that modern married couples are less likely to visit, call, or offer support to parents and siblings than their single counterparts.

Apart from activities with other families when their children are young, married couples are also less likely to hang out with friends and socialise with neighbours. They often distance themselves from single or divorced individuals, even if they were once close to these people. This pattern can come back to haunt them if their own marriage breaks up.

Even as more spouses reported being each other’s close confidants over the past two decades, the number of neighbours, co-workers, club or church members, and extended family with whom Americans discussed important matters dropped sharply. The number of people who reported having four to five confidantes was halved between 1985 and 2004, falling to just 15 per cent of the population. And almost half of all Americans now say that there is just one person, or no one at all, with whom they discuss important matters.

In the UK a British social attitudes survey in 1996 found that almost two thirds of married people or those living together said that their first port of call when depressed was their spouse or partner. Thirteen per cent said they would turn to a friend first. Roughly the same number said they would turn to extended family.

Popular culture is full of advice on how to take our romantic relationships to a deeper level. One common warning is to avoid letting ties to friends or family “interfere” with the time we spend with our spouse. But trying to be everything to one another is part of the problem, not part of the solution, to the tensions of modern marriage.

Through most of history, it was considered dangerously antisocial to be too emotionally attached to one’s spouse, because that diluted loyalties to family, neighbours, and society at large. Until the mid-19^th- century, the word “love” was used more frequently to describe feelings for neighbours, relatives and fellow church members than spouses.

The emotional lives of Victorian middle-class women revolved around passionate female bonds that overshadowed the “respectful affection” they felt for their husbands. Men, too, sought intimacy outside the family circle. A man could write a letter to his betrothed recounting his pleasure at falling asleep on the bosom of his best friend without fearing that she might think him gay. When couples first began to go on honeymoons in the 19^th century they often took family and friends along for company.

But as modern economic and political trends eroded traditional dependencies on neighbours and local institutions, people began to focus more of their emotions on love and marriage. Society came to view intense same-sex ties with suspicion. Psychologists urged people to rebuff family and neighbours who might compete with the nuclear family for attention. In the postwar “Golden Age of Marriage” people began expecting their spouse to meet more and more of their needs.

The weaknesses of this marriage model soon became apparent. Housewives discovered that they could not find complete fulfillment in domesticity. Many men also felt diminished when they gave up older patterns of socialising to cocoon in the nuclear family.

The women’s movement of the 1960s offered a better balance — fairer, more intimate marriages combined with social engagement outside the home. But in the past few decades, our speeded-up global economy has made balance harder and harder to attain, leading us to seek ever more meaning and satisfaction in love and marriage.

I am not suggesting that we lower our expectations of intimacy and friendship in marriage. Instead, I propose that we raise our expectations of other relationships. Emotional obligations to people outside the family can enrich, not diminish, our marital commitments. Society needs to respect and encourage social ties that extend beyond the couple, including those of unmarried individuals, as well as ties between the married and the unmarried.

Taking the emotional pressure off marriage is a win-win situation. The happiest couples are those who have interests, confidants and support networks extending beyond the twosome. And such networks also make single and divorced people better off.

The best protection against the atomisation of modern life is to structure our workplaces and communities in ways that allow people, whatever their marital status, to sustain commitments beyond the couple relationship and the nuclear family. As Coleman notes, “having friendships and social activities other than marriage is not only good for the self and for society, it’s also good for the marriage.”