You could say it was a little hasty.

We met for the first time one muggy afternoon in August on the street outside the Phoenix offices. Our friend Sean made the introduction. Chats by the copy machine and after-work drinks soon followed.

By September, we’d started going to shows together: Nelly Furtado, Jurassic Five, Mos Def. It was all "work-related," multitasking, definitely not dating. But soon enough it was. By November, things were in full swing. "Boyfriend" and "girlfriend" were introduced into casual conversation. Weekend plans were assumed rather than wished for. We started sharing toothbrushes.

In the winter we traveled to New York, where we introduced each other to friends and family. And in the spring, there was a trip to meet the parents. Come June, we found ourselves staring at the bottom line: a lease.

THERE WERE all sorts of seemingly sensible rationalizations for the speedy move-in. There’d been talk of moving to New York back in February — and we’d been planning on finding a place together there. After we decided to stay in Boston, it seemed the natural thing to do; if we were going to live together in New York, why not here? More practically, our leases were up. And since both of us held low-paying jobs, conserving cash was definitely a bonus.

Once we decided to take the plunge, we didn’t pause. Cambridge rents were still prohibitively high, so we started to spend every spare moment reading listings, hoping to find a steal. Anxiety about moving in together was immediately transformed into anxiety about finding an apartment. It was easy that way, manageable; there were answers, rules, quantifiable Things We Could Do.

"We’re looking for a two-bedroom or a one-plus-study in Cambridge for under $1500," we told a broker. "No problem," she cackled, turning around to shake her head at her co-worker, "if you want a place with rats and bugs!" They erupted in laughter. We left.

After checking out one apartment with a floor at a funhouse-like 30-degree slant, another with a 30-minute walk to the closest bus stop, and yet another in a post-collegiate party-building with empty kegs and abandoned futons in the hallway, we were getting desperate.

Just at the point when all was becoming a blur, we met one evening at a building in East Cambridge. It was small, it was musty, it was a mess, it was cheap. In short, it was perfect.

Two hours later we were at the realtor’s office, checkbooks in hand. But something unanticipated happened. Although moving in together had seemed the obvious choice, all of a sudden we were flushed with panic.

"Do you think this is a good idea?"

"Are you sure you really want to do this?"

"Wait, why are we doing this again?"

"This is a good idea, right?"

We lobbed the questions back and forth with increased urgency, like Venus and Serena Williams — except we were sweating more.

"Uh ... yeah," was the conclusion. But it was more of a question. "Yeah?"

Next thing we knew, we were dragging our boxes up a dusty stairwell, choosing sides of the bed, and making coffee for two.

TURNS OUT, we were part of a booming trend. The majority of couples in their 20s and 30s, like us, are currently living together without tying the knot. The number of cohabiting couples of all ages has increased by 600 percent since the 1970s; in the 1990s alone, the number has nearly doubled, from 3.2 to 5.5 million, according to Census statistics.

Back in our parents’ time, moving in together was cause for public shame and family strife, but today it’s practically a rite of passage. America is fast rising to challenge Scandinavia, the cohabitational center of the world, where one-third of all couples live together rather than marry. (Welfare laws in that region give single mothers and cohabiters access to the same benefits married people enjoy in the US: tax exemptions, shared health care, and so on.)

Sociologists attribute the increase in the number of Americans "living in sin" to prolonged post-adolescence. They reason that people are getting married later in life because it takes longer to achieve vocational and financial stability. School drags on over the years; a solid job at a blue-chip corporation has become increasingly difficult to find. As a result, the gap has widened between the age when people become sexually active and the time when they’re in a position to marry. Yet as we date and things become more serious, we desire something deeper.

Over the past 10 to 15 years, notes Marin Clarkberg, an assistant professor of sociology at Cornell University who studies cohabitation, the average age of marriage has risen three years, to 25 for women and 27 for men. "People experience a lot of instability in their 20s," she explains. "Once careers are settled, it becomes much more realistic to think about what it would mean to be married. But before that, it’s very difficult to invest in a long-term relationship."

Not that premarital instability doesn’t cause trouble further down the road, at least for some. Researchers have found that couples who live together before getting married are more likely to be unhappy and less committed, and more likely to divorce than those who choose not to cross the cohabitational threshold. It may seem like fundamentalist propaganda — promoting "family values" through scare tactics — but statisticians and scientists have found it to be true. A research duo who lead Rutgers University’s National Marriage Project, a nonpartisan, nonsectarian initiative, published a paper in 1999 titled "Should We Live Together? What Young Adults Need To Know About Cohabitation Before Marriage." In it, sociologist David Popenoe and social historian Barbara Dafoe Whitehead write: "Most cohabiting relationships are relatively short-lived and an estimated 60% end in marriage. Still, a surprising number are essentially alternatives to marriage and that number is increasing. This should be of great national concern, not only for what the growth of cohabitation is doing to the institution of marriage but for what it is doing, or not doing, for the participants involved. In general, cohabiting relationships tend to be less satisfactory than marriage relationships."

The naysaying convinced Angela, 26, to avoid moving in with her fiancé, Mike, too hastily. Though they had dated for three years, the couple waited to move into an apartment together until three months before their wedding. "I remember hearing about all that in sociology class," she recalls. "That divorce rates are higher for people if they move in together. We didn’t want to rush into anything before we knew our situation."

The same went for Nicole, 27, who recalls being stunned by the statistics presented in a Providence College theology class called Marriage and Family — so stunned that she thought twice about moving in with her fiancé during their year-and-a-half engagement. In the end, they opted to go traditional, literally moving in together right after the honeymoon. "They told us a lot of statistics about divorce, that the Church frowns upon it. Obviously [the professor was] a priest, and he had the Catholic slant on it," she notes. "I don’t necessarily believe all the statistics," she adds with a laugh. "But it would just be my luck."