A study by the Pew Research Center, which uses data from a nationally representative survey of nearly 10,000 Americans over 18 as well as from the National Survey of Family Growth, heralds a turning point in the makeup of the American family. As recently as 2002, those who had lived with a romantic partner (54%) were outnumbered by those who had married one (60%). But now, those proportions are almost reversed, with 59% of Americans having ever cohabited and only half having ever married.

That being said, why do people still tie the knot? To oversimplify in one word, security. The survey’s respondents had notably different levels of trust in their partners.

Two-thirds of the married individuals trusted their partners to tell them the truth but only half of the unmarried did.

Additionally, roughly three-quarters of married folks trusted their partner to act in their best interest but fewer than 60% of the unmarried felt the same way

And while 56% of married partners believed their partners could be trusted to handle money responsibly, only 40% of cohabiters felt the same way.

Scott Stanley, a research professor and co-director of the Center for Marital and Family Studies at the University of Denver, Colorado, who was not involved in this study but has researched cohabiting extensively, says “Marriage has a high signal value as to intention.”

"When somebody tells you, 'That's my spouse,' you know a ton of information about the relationship and the level of commitment," he explains.

“But you could have 10 different couples tell you they’re cohabiting and for some of them it’s like dating with a lot of sleepovers, for others, it’s a lot like marriage in terms of their intention, and for another few, which is the worst deal, it’s one person thinking it’s one thing and the other person thinking it’s not. Cohabitation doesn’t force clarity like marriage does.”

Pew’s researchers also discovered that married couples were more satisfied with how their partners handled most of the usual couple chafing points: parenting, chores, work-life balance, and communication.

In bed, it was too close to call and a bit sad: just 36% of married Americans and 34% of those living together are very satisfied with their sex lives.

While nearly all of those surveyed named love and companionship as one of the major reasons for sharing their residence, those who were not married were more likely to cite financial pressures, convenience, and pregnancy as big motivations for moving in with each other.

As Stanley points out, money also keeps some people in cohabiting relationships when they don’t want to be. “In particular we find that when women say they’re moving in for reasons of financial convenience, that’s associated with negative characteristics of relationships," he said. "It’s like, ‘I wouldn’t be here if I could afford to live on my own.'”

His research also suggests that the common opinion that people should live together to test the relationship is ill-founded. "Over seven published studies, we’ve found that living together before you’re engaged is just riskier," he explained.

So is all the trouble worth it? Last year, the University of Chicago economist Sam Peltzman published a study in which he found that marriage was "the most important differentiator" between happy and unhappy people.

Married people are 30 points happier than the unmarried — income contributes to happiness, too, but not as much.

Sociologist and professor at the University of Virginia Brad Wilcox agrees. In his book 'Get Married: Why Americans Must Defy the Elites, Forge Strong Families, and Save Civilization', he writes that "Marital quality is, far and away, the top predictor I have run across of life satisfaction in America. Specifically, the odds that men and women say they are ‘very happy’ with their lives are a staggering 545 percent higher for those who are very happily married, compared with peers who are not married or who are less than very happy in their marriages."

So maybe chipping away a few hills of clothes along the way is worth it.