Actually, if the strike threat hadn't spurred us to set up housekeeping, something else would have. By then, we were 99 percent sure we'd marry some day -- just not without living together first. I couldn't imagine getting hitched to anyone I hadn't taken on a test-spin as a roommate. Conjoin with someone before sharing a bathroom? Not likely!

With our decision to cohabit, we joined the mushrooming ranks of Americans who choose at some point in their lives to inhabit a gray zone -- more than , less than , largely without legal protections. Thirty or 40 years ago, cohabitation was relatively rare, mainly the province of artists and other questionable types, and still thought of as "living in sin." In 1970 only about 500,000 couples lived together in unwedded bliss.

Now, nearly 5 million opposite- couples in the United States live together outside of marriage; millions more have done it at some point. Some couples do choose to live together as a permanent alternative to marriage, but their numbers are only a tiny fraction: More than 50 percent of couples who marry today have lived together beforehand. (At least 600,000 same-sex couples also cohabit, but their situation is different, since most don't have the choice to marry.)

"It's not this bad little thing only a few people are doing," says University of Michigan sociologist Pamela Smock. "It's not going away. It's going to become part of our normal, typical life course -- it already is for younger people. They think it would be idiotic not to live with someone before marriage. They don't want to end up the way their parents or older relatives did, which is ."

In my and my husband's case, the pre-matrimonial experiment seems to have worked out well. But according to recent research, our year of shacking up could have doomed our relationship. Couples who move in together before marriage have up to two times the odds of divorce, as compared with couples who marry before living together. Moreover, married couples who have lived together before exchanging vows tend to have poorer-quality marriages than couples who moved in after the wedding. Those who cohabited first report less satisfaction, more arguing, poorer communication and lower levels of commitment.

Many researchers now argue that our penchant for combining households before taking vows is undermining our ability to commit. Meaning, the precautions we take to ensure marriage is right for us may wind up working against us.

From toothbrush to registry

Why would something that seems so sensible potentially be so damaging? Probably the reigning explanation is the inertia hypothesis, the idea that many of us slide into marriage without ever making an explicit decision to commit. We move in together, we get comfortable, and pretty soon marriage starts to seem like the path of least resistance. Even if the relationship is only tolerable, the next stage starts to seem inevitable.

Because we have different standards for living partners than for life partners, we may end up married to someone we never would have originally considered for the long haul. "People are much fussier about whom they marry than whom they cohabitate with," explains Paul Amato, a sociologist at Penn State University and one of the theory's originators. "A lot of people cohabit because it seems like a good idea to share expenses and have some security and companionship, without a lot of commitment."

Couples may wind up living together almost by accident. "People move in their toothbrush, their underwear, pretty soon a whole dresser," says Marshall Miller, coauthor with his partner, Dorian Solot, of Unmarried to Each Other: The Essential Guide to Living Together as an Unmarried Couple. "Then someone's lease is up and since they're spending all their time together anyhow... "

Or, two people may move in together without a firm future plan because one partner isn't sure the other is good marriage material: He drinks too much; she gets really nasty during fights. Rather than commit, they take a trial run. Once they've shacked up, relatives start noodging: "So when are you going to get married already?" At friends' weddings, people ask, "When will it be your turn?"

"There's an inevitable pressure that creates momentum toward marriage," says Amato. "I've talked to so many cohabiting couples, and they'll say, 'My mother was so unhappy until I told her we were getting married -- then she was so relieved.'" On top of the social pressure, Amato points out, couples naturally start making investments together: a couch, a pet -- even a kid. Accidental pregnancies are more common among cohabiting couples than among couples who don't live together.

Once their lives are thoroughly entangled, some couples may decide to wed more out of or than love. "I know a lot of men who've been living with women for a couple of years, and they're very ambivalent about marrying them," says John Jacobs, a New York City psychiatrist and author of All You Need Is Love and Other Lies About Marriage. "What sways them is a feeling they owe it to her. She'll be back on the market and she's older. He's taken up a lot of her time." Women in particular may be afraid to leave an unhappy cohabiting relationship and confront the dating game at an older age. "If you're 36, it's hard to take the risk of going back into the single world to look for another relationship," says Jacobs.

Charles, a 44-year-old New Yorker (who asked that his name be changed), admits that in his 30s, he almost married a live-in girlfriend of three years for reasons having little to do with love. The two moved in together six months after meeting when his sublet came to an end. "I thought it probably wasn't the best idea, but it was so much easier than looking for an apartment," Charles says. "I told myself: 'Keep trying, and maybe it will work.'"

Eventually his girlfriend insisted they either marry or break up, and he couldn't find the strength to leave. The two got engaged. Weeks before the date, Charles realized he couldn't go through with it and broke off the engagement. "Her father told me, 'I'm sorry horsewhips are a thing of the past,'" Charles recalls, still pained by the . Even now, he regrets moving in with her. "It was a terrible idea," he says. "You get entwined in each other's lives. If you're not sure you want to be entwined, you shouldn't put yourself in a position where it's definitely going to happen."

Some evidence indicates that women have less control over the progress of the cohabiting relationship. She may assume they're on the road to marriage, but he may think they're just saving on rent and enjoying each other's company. Research by sociologist Susan Brown at Bowling Green State University in Ohio has shown there's a greater chance cohabiting couples will marry if the man wants to do so. The woman's feelings don't have as much influence, she found: "The guy has got to be on board. What the woman wants seems to be less pivotal."

Cohabiting men may carry their uncertainty forward into marriage, with destructive consequences. A 2004 study by psychologist Scott Stanley, based on a national phone survey of nearly 1,000 people, found that men who had lived with their spouse premaritally were on average less committed to their marriages than those who hadn't. By contrast, cohabitation didn't seem to change how women felt about their partners.

Based on this finding and others, Stanley, director of the Center for Marital and Family Studies at the University of Denver and another originator of the inertia theory, believes women should be especially wary of moving in before getting engaged. "There are plenty of young men who will say, 'I'm living with a woman but I'm still looking for my soul mate,'" he says. "But how many women know the guy is thinking that way? How many women are living with a guy thinking he's off the market, and he's not?" Men also get trapped in troubled relationships, admits Stanley, but women are more likely to bear the brunt of ill-considered cohabitation decisions for the simplest reason -- they are the ones who have the babies.

The cohabiting type

The inertia theory is not the only way to explain why couples who move in before marriage are less likely to stick it out for the long haul. There may also be something specific about the experience that actually changes people's minds about marriage, making it seem less sacrosanct. "A couple of studies show that when couples cohabit, they tend to adopt less conventional beliefs about marriage and divorce, and it tends to make them less religious," says Amato. That could translate, once married, to a greater willingness to consider options that are traditionally frowned upon -- like saying "so long" to an ailing marriage.

Nonetheless, there's a heated debate among social scientists about whether the research to date has been interpreted properly or overplayed to some extent. Having a family income below $25,000, for example, is a stronger predictor of divorce in the first 15 years of marriage than having shared a premarital address. "Having money, a sense of an economically stable future, good communication skills, living in a safe community -- all of those things are more important," says Smock.

Because it's impossible to directly compare the effects of marriage and cohabitation, there's just no way to prove cohabiters' higher divorce rates aren't a side effect of their other characteristics, says psychologist William Pinsof, president of the Family Institute at Northwestern University. They may just be less traditional people -- less likely to stay in an unhappy marriage in observance of religious beliefs or for the sake of appearances. "Those who choose to live together before getting married have a different attitude about marriage to begin with. I think cohabiting is a reflection of that, not a cause of higher divorce rates," he says. One population of cohabiters also tends to have less money and lower levels of , which in itself can strain a relationship.

In short, not everyone buys the idea that cohabitation itself is hazardous to your relationship. For some couples, it may serve a useful purpose -- even when it lacks a happy ending. About half of all cohabiters split up rather than marry, and many of those splits save the parties involved from rocky marriages, miserable divorces or both.

That's the attitude Amy Muscoplat, 34, a children's librarian who lives in Santa Monica, California, now has about the man she lived with several years ago. She and Mr. X had dated for nine months when they got engaged; a few months later she gave up her rent-controlled apartment by the beach, sold most of her furniture, and the two moved in together. "We moved in in August, and by early September he flipped out," she says. "We were supposed to get married in early November. The invitations had gone out, and then he changed his mind. Living together was the reality check for him, the mirror that made him go, 'Gosh, this might not really work for me.'"

Though she and her family lost thousands of dollars when the wedding was called off, Muscoplat is things fell apart when they did. If they hadn't moved in together, she says, "I think he might have been pushed to the same place at some later point, maybe some day down the road when I was . I have a religious take on it -- God was really watching out for me and I dodged a bullet."

The debate over cohabitation is partly a rehash of the values and morals conflicts that tend to become political footballs in America today. But on one point, virtually all researchers agree: We need to understand the effects of cohabitation on children. Some 40 percent of all cohabiting households include kids -- that's somewhere close to 3.5 million children living in homes with two unmarried opposite-sex grown-ups.

Cohabiting relationships, by their nature, appear to be less fulfilling than marital relationships. People who cohabit say they are less satisfied and more likely to feel , Susan Brown has found. While the precarious finances of many cohabiters has something to do with it, Brown also points to the inherent lack of stability. Long-term cohabitation is rare: most couples either break up or marry within five years. "Cohabiters are uncertain about the future of their relationship and that's distressing to them," she says.

As a result, cohabitation is not an ideal living arrangement for children. Emotionally or academically, the children of cohabiters just don't do as well, on average, as those with two married parents, and money doesn't fully explain the difference. The of in a shakier living situation may be part of the problem, says Brown. "Stability matters. It matters for the well-being of children and adults alike," she adds. "We're better off with commitment, a sense that we're in it for the long haul."

The must-have discussion

Cohabitation rates may be skyrocketing, but Americans are still entirely enchanted with marriage. That's a sharp contrast with some Western societies -- Sweden, France or the Canadian province of Quebec, for example -- where cohabitation is beginning to replace marriage . In the United States, 90 percent of young people are still expected to tie the knot at some point.

Since most Americans are destined for marriage -- and a majority will live together beforehand -- how can we protect against the potentially undermining effects of cohabitation? Follow the lead of one subgroup of cohabiters: Those who make a permanent commitment to each other first. One study that tracked 136 couples through the initial months of marriage found that early intentions seem to make a big difference. About 60 of the couples in the study lived together before getting engaged, while the rest waited either until after they were engaged or after they were married to set up housekeeping. Ten months after the wedding, the group that had cohabited before being engaged had more negative interactions, less about the relationship and weaker feelings of commitment than the other two groups. But the marriages of couples who had moved in together after getting engaged seemed just as strong as those who had moved in together after marrying.

Among other things, couples who get engaged before cohabiting probably have a clearer understanding of each other's expectations before they combine households. On that point, Mia Dunleavey, a 39-year-old online financial columnist living in Brooklyn, New York, can speak with the sadder-but-wiser voice of experience. In her late 20s, Dunleavey was involved with a man she hoped to marry. He reluctantly agreed to move in with her, spurred by the fact that his lease was running out, but he vacillated for so long about setting a wedding date that she finally ended the relationship. Soon after, she relocated across the country to move in with a new man she'd fallen in love with, only to find their living styles were utterly incompatible.

Back in New York again, she took stock. "I was terribly disappointed," Dunleavey says. "You have this faith that you're moving in with someone in order to deepen the commitment, and it doesn't necessarily happen at all. Those two things are not correlated.

"At that point, I said, 'Never ever, ever again,'" she continues. "Living together is a waste of time and energy. The piece of china you'd gotten from your mother gets broken in the move. My living-together experience was a catalog of lost and broken things, never mind my heart."

When she fell in love again, she did things differently. She moved in with her intended just two weeks before the wedding -- because by that point, there was no question about their future together. "There was no take-it or leave-it," she says. "The commitment was the foundation of the marriage. Alas, my only experience of living with someone is that when you leave the door open for quasi-commitment, quasi-commitment is what you get."

Miller and Solot don't advise against cohabitation for couples without immediate plans to marry. But they do believe each partner needs to understand clearly what the other is thinking. "The most important thing is for people to treat moving in together as a serious decision, a major life choice," Miller says. "What does it mean to you both for the long and short term? If one person thinks living together means a quick path towards marriage and the other thinks it's just saving on rent and having a friend with benefits, there could be trouble. The important thing is to be on the same page."

As for my husband and me, we had this much going for us when we moved in together: We'd already discussed a lot of the important issues. We knew we wanted similar things: a family; a "for better or worse" kind of commitment; a partner who knew life had to stop on Sundays, when Six Feet Under or The Sopranos was on. Even before the ring, it was clear to me I'd found someone who'd be willing to work things through. And he has been.

Perhaps there's hope for us after all.