You've heard it said: Never let a hot date come between you and your friends. And it's not bad advice, per se. But there comes a point — usually somewhere around the exchanging of vows — when that aphorism stops being applicable.

When you get married, you aren't just gaining a spouse; you're getting all their current and future friends, too. Keeping, and making, friends as a pair can be a lot more complicated than going it alone, but friendship experts say it's possible. All you need is some new advice.

Quality vs. quantity: Your early 20s are sort of the golden age of friendship, says Ray Pahl, a sociology professor at England's University of Essex and co-author of "Rethinking Friendship" (Princeton University Press, 2006). Young professionals spend these years wrapped in a cozy bubble of college and urban living, surrounded by a large network of friends who serve as a surrogate family.

Getting married, which often entails graduating, buying a house or otherwise moving out of these enclaves, can send people into fits of insecurity as they try to hang on to every best bud and convivial acquaintance — and, in the process, spread themselves too thin to maintain any of those relationships well.

"You actually have to be a bit ruthless and think clearly," Pahl says.

His advice is to look at your friend group, figure out who you really want in your life 10 years from now, and put your energy into remaining close to them.

"It's really not cynical or calculating," he says. "You owe it to the ones that really matter to give them your time."

You don't have to like all his friends: "This is one of the most serious ways in which people can lose friends," Pahl says. "Two women might be great friends alone, but because one's husband is a class rear end, the friends can start to feel ill-at-ease with each other."

But, the experts say, you don't necessarily have to choose between your friendship and your marriage.

"Most of the time, there is just a spoken or an unspoken agreement that the friendship can continue as long as the spouse is not expected to be part of that friendship, and the friendship doesn't cause the spouse to feel like he or she is second to the friend," says Jan Yager, a sociology professor at the University of Connecticut who has been studying friendship and relationships for more than 10 years.

She and Pahl both advise discussing the situation with your spouse, explaining how and why this friend is important to you, and then arranging things so you can spend time with your friend but your spouse doesn't have to.

One caveat: In some cases, the friend vs. spouse hatred might be so strong that you really do have to make a choice. Tanya Noreen, a 35-year-old Canadian who lives in Hong Kong, recently ran into a problem like this with her husband of seven months and one of his particularly toxic friends.

"There are friends I would fight to keep within my relationship," she says. "But if they caused problems in my marriage, I would have to limit my time with them."

It's up to you to make your single friends feel welcome: There's definitely a different dynamic to hanging out with a couple than getting one-on-one time with a friend. And other factors can also make single friends uncomfortable.

For instance, Pahl points out that priorities and interests often change after you get into a long-term relationship, making it harder for you and your single friends to relate. And, according to Yager, single friends often perceive a difference between couples who are dating and couples who are married. In the latter case, she says, it's common for a singleton to feel like they're intruding, or feel more like a third wheel than they did before.

This is where you come in. If you have a single friend you want to hang on to, it's up to you to integrate them into your new life. Pahl recommends making sure you still spend some time with your friend alone, so they know they're still important.

Non-experts have some advice as well. Rebekah Tilley, a 28-year-old communications director from Lexington, Ky., says that when she's out with single friends, she tries to make sure she doesn't spend the whole evening talking about her husband.

"I put myself in their shoes and think, 'Would I care about this?' " she says.

And, Tilley adds, it's the responsibility of any good host to make sure they don't invite only one single person to a party of couples.

Couples need some time apart: This might be the most important post-marriage friendship advice. According to Pahl, research he did for a cruise line called Ocean Village showed that not only are more people leaving behind their spouses to take vacations with same-sex friends, but doing so can actually strengthen marriages.

First, spending time apart gives couples a way to vent and seek relationship advice from friends. Second, Pahl says, relationships that are insular tend to be the most vulnerable. Spending time apart means you trust your spouse and yourself. And finally, doing things separately gives a couple new things to talk about and new ways to bond.

Tilley agrees. "Spending time apart makes you appreciate the other person more," she says. "I can get a good look around and think, 'Yeah, I remember why I'm with you.' "