THINKING ABOUT moving in together? You’ll find everyone has an opinion. Parents, friends, grandma: they all chip in with horror stories and instructions. Even a potential landlord hammered us with questions about the stability of our relationship. "I need to make sure one of you can cover the rent if the other moves out," she said, unflinchingly. We looked at each other, cringing. "Uh, yeah. We don’t think that’s going to happen."

And then there’s that family pressure. "Why move in together when you could just get married?" was a nagging refrain. We still hear it. Usually, we just demure and try to explain that this is what felt right for us. "I’m not ready to be a missus yet," Nina often replies. "I can’t imagine myself being one of those ‘married friends.’ "

Jaclyn Geller, author of Here Comes the Bride: Women, Weddings, and the Marriage Mystique (Four Walls Eight Windows, 2001), calls it The Culture of Advice, wherein those who are married or engaged feel free to share their ideas — and strong opinions — without restraint. "There’s a chorus of experts telling us how to conduct our private emotional lives," Geller says via phone. "It’s an advice industry; it all has a kind of dull sameness. For women it tends to be, ‘Get that ring on the finger before you move in.’ And for men it’s, ‘Stop sowing those wild oats.’ "

Kelly, 27, is about to move to Los Angeles with Gary, 28, her boyfriend of three years. Here on the East Coast, they’ve been commuting nightly between Dorchester and Cambridge, but the couple is planning to share an apartment in California — a development Kelly’s mother is none too pleased about. "My mother is not particularly supportive in terms of living together before marriage," Kelly explains. "She has this whole idea of, ‘Why buy the cow if you can get the milk for free?’ "

The bovine analogy is a ’50s-era holdover that’s made a comeback among twentysomething women, suggesting that men, just out for sex, won’t spring for a ring if they’re already getting laid. "Even though I know that’s not the situation with my relationship, it makes me wonder," Kelly admits.

It’s not only religious constraint or pressure from grandma that keeps couples from cohabiting. Some couples, like Nicole and her husband Donovan, simply prefer to wait. "He carried me over the threshold," she says, giggling. Afraid of becoming too comfortable without the marriage contract, which in turn could prolong the engagement, Nicole was happy to keep separate apartments. "You still learn about each other," she maintains.

While Nicole says she respects other people’s choices to move in together before marriage — "I’m not, like, ‘You sinners!’ " — she wonders aloud about the challenges cohabiters like us might face. "I think it would be hard in your situation," she says, later adding, "good luck!"

Certainly, we had some concerns. Most significantly, if the relationship was going so well, why tempt fate by upping the ante? Breaking up sucks, but breaking up/moving out/dividing belongings/finding a place to live sinks to another level of relationship hell. During the first few months of getting settled in our new apartment, we each bought items separately, keeping track of who owned what in case (God forbid) things didn’t go as planned. Michael owns the armoire. Nina owns the kitchen table. Michael owns the couch. Nina owns the coffee table. Then, at a certain point, we just stopped remembering.

"Somehow there’s this thought that if you live together, you’re going to mess up your relationship," says Marshall Miller, co-founder of the Alternatives for Marriage Project (AMP), a national nonprofit based in Boston that provides support to cohabiting couples. "Cohabitation in itself is not going to do that. What’s going to do that is not having conversations about what your expectations are."

Miller and his partner, Dorian Solot, who will say only that they are "in their late 20s," run a Web site for the AMP (www.unmarried.org) where they provide resources for cohabiters. Solot carves a full-time job out of her role at the AMP. Miller and Solot, who are currently writing a book on cohabitation, take the idea of shacking up to rhetorical and political extremes. In an interview with the Phoenix a year and a half ago, the pair explained their unusual arrangement: both bisexual, they were in an "open" relationship, according to Solot. Whether or not that is still the case, both are enthusiasts for nonmarital living. "When our friends move in together, we send them a note that says, ‘Congratulations on your cohabitation!’ " says Miller, who adds that he’s not "anti-marriage," but rather "pro-cohabitation."

For Miller and Solot, who laughingly explain that their current project precludes their ever getting married, cohabitation is more than just a living arrangement or a testing ground for tying the knot — it’s a political statement, a lifestyle choice, and a pulpit. For most couples, though, it’s a matter of neither religion nor politics. Rather, it’s an unquantifiable mix of love and simple common sense.

In most cases, the initial impulse is romantic and emotional. But the bottom line can be awfully compelling, too. "Saving on rent is a great benefit to cohabitation," agrees Miller, who has lived for seven years with Solot. "The truth is," says author Geller, who lived with a boyfriend for four years, "a lot of people move in for financial reasons. It’s extraordinarily expensive to live on your own."

And rent isn’t the only thing that’s divided. Cable, phone, food — it’s all easier to bear when two are footing the bills. Added perks include joint music collections, electronic gear, magazine subscriptions, and stacks of books.

It also makes sense for logistical reasons. Before moving into the same abode, we were spending as many as five nights a week together, commuting from Somerville to Allston. Preparing sleepover bags, arguing about who was staying where, and studying bus schedules became a daily ritual, one that we were extremely pleased to leave behind.

"We were kind of sick of making plans," says Geller, of her reasons for shacking up with her now-ex, "of always having to talk and make a plan for dinner. It seemed like a nice idea just to have the person be there. Life becomes less about logistics. If you don’t make a plan, there’s always seeing each other in bed that night. There’s built-in contact."

But moving in together also raises a host of new mundane concerns. Everything from divvying up chores to paying bills to setting the alarm can cause friction. Friday nights spent in front of the TV become a weekly habit, old friends stop calling, and that initial effervescent rush gives way to everyday familiarity, along with occasional feelings of annoyance.

Moving in together is similar to a business merger, rife with negotiation, compromise, and payoff. Making it work takes more than just feelings of love or sexual attraction. It takes dealmaking, power dinners, and space management.

AUGUST 11: move-in day. From Day One, negotiations reached a fever pitch matched only by proceedings at the UN. Michael was concerned that the pale shade of gray we’d painted the living room looked decidedly more baby blue on the wall — a feminine touch that made him none too happy. As the hours passed and the paint dried, Michael’s face soured. We solved the issue by bringing together all our willing friends and asking for their opinions. "I guess it’ll grow on me," Michael sighed.

From decorating to standards of cleanliness to cooking, each room — indeed, each sphere of cohabitation — was fraught with compromise between personal preferences.

Agenda Item #1: the living room. "Why should I buy another couch if I have a perfectly good futon, which folds into a nice couch?" Michael wondered. We were at a standstill. And so it was: we carted the large blue futon with metal arms up a flight of stairs. In our tiny apartment, it took up the length of a whole wall. Nina huffed: too ugly, too bulky, too uncomfortable, and too, er, blue. Michael stood firm.

The futon sat there for a week. We steamed, back and forth, arguing need versus want, spending versus saving, futon versus non-convertible furniture. In the end, Michael sold his futon to another couple and we bought a couch at Pier One. It converts.

On another issue, Michael won. He’s a freelance music writer, so every day is like Christmas as he tears through CD mailers, chucking the empty packages on the floor around him. CDs rule in our apartment. Like ants, they appear en masse and collect in every corner. Michael sees a blank wall like a person desperate for parking sees an open curb: prime space. "More room for CDs," he says with a slow grin. Nina has come to rue the daily CD arrivals. "The CDs are everywhere," Michael boasts, adding, "and you can’t stop them." And so they sit, piled up on every available surface, including the new couch.

Agenda Item #2: the bedroom. Michael often reviews concerts late, returning home after midnight. Nina prefers tucking in at the matronly hour of 11 p.m., waking up the next morning at 7:30. This became a big issue for us. We tried going to bed at her hour, but he couldn’t fall asleep. Then we tried going to bed at his hour and waking at hers. Bleary-eyed for weeks, bedtime moved to the forefront of our negotiations. These days, we generally settle on 12 and call it a night.

Geller found bedtimes to be a problem with her boyfriend as well. She was in graduate school, while he had a nine-to-five job. "You’re in a very different rhythm, a very different schedule than someone who has an office job," she says. "I was really shocked by how much negotiation there was."

Agenda Item #3: the kitchen. Craig and his girlfriend moved in together when they started graduate school in New York. He has a penchant for all-beef patties. She’s increasingly watchful about what she eats: vegetarian, no processed sugar, all whole grains. She doesn’t eat sushi anymore because of the rice. Craig has struggled to satisfy his cravings for fast food, carbs, and cocktails while respecting his girlfriend’s dietary rules.

Agenda Item #4: the bathroom. Lisa thought she knew a lot about her fiancé, Ethan, before they moved in together. They’d been spending every night together for months. But there was one thing she didn’t know. "Every time he takes a shower, he uses a new towel," she sighs. "By the end of the week, there are five towels on the floor. I don’t want to wash five towels every week. I told him to pick a towel and stick with it all week."

We have a similar duel. Michael detests doing laundry. So we divvied up chores accordingly: Michael does grocery shopping and Nina does laundry, a task she sort of enjoys. But Michael’s laundry loathing runs so deep that even the idea of removing his folded, clean clothes from the basket has the same effect as nail screeches on a chalkboard. And so they sit and sit, for days, until desperation for socks necessitates emptying the basket. Or until Nina loses it.

Josh had been living in his apartment for 18 months when his girlfriend Sarah moved in. There were still boxes filled with his books strewn all over the living room. His laundry was stashed in a gym bag. Sarah hightailed it to Target, investing in an "apparatus" for the bathroom, bookshelves, and a laundry basket. "Now I have to put my dirty clothes in this wicker thing," Josh explains, pausing to wonder aloud, "Come to think of it, where did that thing come from?"

FLOSSING, PEEING, checking yourself out in the mirror ... just being. When you move into a one-bedroom apartment with no doors between the rooms, everything becomes public, from phone conversations to private moments at the bathroom sink. Sometimes, when you’re having an extended sit in the restroom, you just don’t want someone to ask, "Are you okay?" when you come out for air.

"I’ve talked to my women friends," says Geller, "and some of them can go to the bathroom in front of their boyfriends and husbands. I never could. I’m a really private person." Even talking on the phone can become an issue. "There’s this idea that you’re [supposed to feel comfortable] looking at this person with spittle on your face in the morning," laughs Geller. "I think there’s something to be said for solitude, privacy, seeing that person when you want to be seen."

At first we were a little shy, sheepish. Holding in our bodily noises, excusing ourselves at every turn, blushing profusely. One evening, we were sitting at the kitchen table eating dinner and there was a loud rrrrippp. We stayed silent, waiting for the other person to make some sort of excuse, perhaps apologize.

"So is that, like, now acceptable?" Nina finally asked. "Yeah, I was wondering the same thing," Michael responded. We squinted at each other, still waiting for the other to claim ownership of the flatulence.

And then ... RRRRIPPP. We heard the sound again — from upstairs. It was our clod-footed neighbor pushing chairs around his hardwood floors. We shared a sigh of relief. Here was one cohabitational hazard that we didn’t have to discuss any further. No negotiation needed, no compromise necessary. Our efforts were united; we could gang up together, on someone else.

Nina Willdorf can be reached at nwilldorf[a]phx.com and Michael Endelman can be reached at mikeendelman@yahoo.com