Here are seven tips to help you survive under the same roof.

1. Your relationship will change
Now that you're "domestic partners", things are going to be different around here, mister. Effective immediately.

"Cohabitation," explains Marshall Miller, co-author of Unmarried to Each Other: The Essential Guide to Living Together as an Unmarried Couple (www.amazon.com) "is a lot like turning the TV to your favourite channel - and then leaving it on 24-7. You're bound to see some stuff you don't like so much."

For one thing, your beloved won't always look as hot as she used to when you picked her up on a Saturday night.

Yes, that gorgeous lady is still in there somewhere, but now you'll have to get acquainted with the stinky chick who just came home from the gym and the irritable woman who's too preoccupied with the Brown account to succumb to your frisky antics. Know this and accept it before going in.

2. Your sex life will definitely change, big-time
Not every night will end with the two of you naked, sticky and sweaty. "When you live apart, you make time for sex - any minute you can get your hands on each other, you do," says Logan Levkoff, a sexologist and advice columnist.

"But when you're around one another all the time, the frequency of sexual activity may taper off.

"The solution," advises Levkoff, "is still making time for intimacy, but changing your expectations. Realise that you can be intimate without having intercourse."

This means you'll need to accept the transition from hardware to software - less bonking, more cuddling.

3. Gentlemen, start your Squeegees
Dividing up domestic chores is one of the first things a cohabiting couple needs to discuss. And forget equality.

"Everything doesn't have to be fifty-fifty," according to Dr Andrew Cherlin, author of The Deinstitutionalization of American Marriage and Public and Private Families: An Introduction (McGraw Hill).

"If one of you works 50 hours a week and the other 25, there's nothing wrong with the less busy person taking on more of the housework."

You can reduce the tension and tedium by volunteering for housework that doesn't drive you crazy. My mate Josh hates washing crockery, but unlike most people, he doesn't mind scrubbing pots and pans.

So after dinner he gets stuck into the heavy metal, while his wife merrily tends to the flatware. It's compromises like this that make a relationship work.

4. Love is annoying
It's inevitable: now that you're living together, you're gradually going to discover each other's irritating habits. She makes a weird grunting noise while she sleeps; you fart with abandon.

"One way to soften the blow is to try living together for a spell before you actually move in," Levkoff advises. "Just make sure it's a normal, mundane week so you'll get a real feel for what the morning rush is like, what the dishwashing situation is like."

The key, no matter how long you've been living together: when confronted with one of those fingernails-on-the-chalkboard-of-life moments, don't let it slide. But resist the urge to bite her head off.

Wynne Whitman, co-author of Shacking Up (www.amazon.com), prefers a gentler, more constructive approach. "Instead of yelling, 'Why the hell do you always leave your briefcase on the floor?' try saying, 'It makes me very happy when you put your briefcase away.'

This phrasing makes your flatmate think she's doing you a favour and it doesn't seem like a chore."

5. You're not engaged - yet
There is a subtext to this move. According to the Annual Review of Sociology, about 75 per cent of cohabiting couples say they plan to marry their partners.

In addition, 55 per cent of marriages today are preceded by cohabitation. But not every live-in couple is destined to walk down the aisle together.

"We interviewed a woman who assumed that moving in with her boyfriend was an engagement," Whitman recalls. "But she never actually spoke to her boyfriend about it. When she found out he didn't want to marry her, she was heartbroken."

Like it or not, when you move in with your girlfriend, you're sending the "I'm ready to settle down" message. So, unless you've made it clear that living together is not a formal engagement, she's likely to think there's a diamond ring in her immediate future.

6. You two may not be married, but your problems are wedlocked
Live-in couples have to deal with many of the same issues as spouses.

One of the thorniest is keeping the relationship fresh. Because you're no longer dating, it's crucial that you maintain the relationship's fun factor. For starters, don't become too reliant on one another.

"It's really important not to put all your eggs in one basket," stresses Whitman.

"Often, people make the mistake of giving up all their other relationships just because they're living with someone. You need to spend time apart to appreciate the time you spend together."

7. Live and learn - together
You may discover, as I did, that your girlfriend's good qualities more than make up for her uselessness as a mover. Or you may find that her insistence on replacing the toilet-paper roll so it feeds from the bottom is too much for you to take. Either way, you're in this together.

Find a way to get over, through or around every obstacle and your relationship may evolve into something even more wonderful than convenient sex.

"There's a misconception that people who cohabit never want to get married," says Whitman.

"I disagree. I think, on the contrary, they want to make sure they have only one marriage. They want to make sure this is the right person before they commit."

And before they have to lug all those boxes back down 13 flights of stairs.