2 The Bootie-Based Marriage

Maybe things aren't perfect between you, but she's got nothing to complain about in the bedroom department. You have sex almost every night, often experimenting with new locations, positions and toys. Once in a while she suggests that she'd like to slow down and spend an evening just talking or cuddling. But at least you're sure she has no reason to get the nookie somewhere else.

Will she cheat? The chances are better than you think. While men sometimes sleep with other women because they're looking for a sexual thrill--you know who you are, Stan Lewhorski of Mason, Mich.--that's seldom the reason women have affairs. And while good sex is an important part of marriage, sometimes a woman will feel her husband is focusing on sex too much, says Markman. "It seems to be all about sex, not enough about romanticism."

Avoid the horns: She may want nookie as much as you do, but she still needs reassurance that the sex is an expression of your feelings for each other and not just a way to get your rocks off. "A woman wants to be wooed on a daily basis; she wants her boyfriend or husband to let her know in a way that's meaningful that he loves or cares about her and is attracted to her," says Markman. If she starts to feel she'll never get that romance from you, she may turn to a "friend" who seems to understand her better. And while that outside relationship may or may not ever progress to sex, it's sure to be harmful to your marriage.

3 The Working Wife

She's gone back to school or work and is meeting lots of new, interesting people, including plenty of men. At night, she talks about the new things she's learning and experiencing. Finally, you tell her that the idea of her being around so many men during the day is starting to bug you. She assures you that you have nothing to worry about.

Will she cheat? Probably not. While work or school would give her more opportunity to find someone else if she were actively looking, it's more likely she's concentrating on her career or academic responsibilities, Markman says. "The fact that she's around other men won't mean much if she's happy in her relationship with you," he adds. And if she's discussing her daily activities with you, it shows she wants to bring her new experiences into the relationship rather than use them to provide an escape from it.

Avoid the horns: Of course, Markman adds, it's natural for you to worry when she enters a new stage in her life, but discussing your fears with her rather than turning into a jealous jerk is likely to make your marriage stronger. In fact, she'll probably be so happy that you actually initiated a relationship talk on your own, you'll get brownie points for days.

4 The Restless Relationship

Since the baby was born a couple of years ago, you haven't been very happy at home. Your wife still hasn't taken off all her pregnancy weight, and you can't remember the last time the two of you had sex on a weekday. You're working your butt off to provide for everyone, and yet she still complains that you aren't helping out enough around the house. In fact, other women are starting to look pretty good to you; there's a certain young associate you've been flirting with at work, and who knows where that will lead?

Will she cheat? She damn well might. A tough period in a relationship doesn't mean she's going to have an affair, but it becomes more likely if you go out looking to meet your own needs and no longer seem to care about hers.

"Every marriage goes into the doldrums at some time," Lusterman says. "It may be when a child is born and the man feels left out of things, or the woman feels he isn't participating enough. And it can happen with a dual-occupation couple if there isn't enough leisure time together, or when a woman becomes more specialized in child-rearing and there's more burden on the man to produce income. If you're sensitive to that, you can talk about it. Unfortunately, often a woman will try to talk about it but feels unheard."

Avoid the horns: If you respond to your own marital dissatisfaction by pulling away rather than dealing, it's likely that she will too, and neither of you will get what you want. The fact that you yourself are tomcatting around should be a warning sign that you probably don't have the first clue about what she's doing either, Lusterman says. If you're behaving this way, then it's time to stand back, have a good look at the issues you're hiding from, and put your energy into your marriage instead of into seducing the next ex-Mrs. You.

PREVENTING TROUBLE BEFORE IT STARTS

There's no such thing as a relationship without problems. But most can be solved if you're willing to put in some effort, the experts say. It's when you ignore trouble on the horizon, or stop caring enough to do anything about it, that disaster is likely to strike. "If you're convinced she's having an affair, she's probably having one," Lusterman says. But if you pay enough attention early on, you can probably fix what's wrong long before it gets to that point.

"The most important thing for an affair-proof marriage is that both people are very engaged in the relationship, committed to it and take pleasure from it," Lusterman says. "If you don't have that, you really need to get to work."

IS SHE CHEATING?

How do you know if your wife or girlfriend is having an affair, or at least seriously thinking about it? To find out, we went to investigator Anthony DeLorenzo, co-author of 28 Tell-Tale Signs of a Cheating Spouse:

1. There's no communication at home. "If she isn't talking to you, she's talking to someone else," DeLorenzo says.

2. She avoids having sex with you. "Since women have affairs for love, not sex, she won't sleep with her husband unless she's forced to."

3. She has a male "friend" who's a good listener. "Even if she isn't doing anything yet, he knows he's first in line."

4. She works a lot of overtime or leaves early in the morning. "Most of the time, people who have affairs will cheat with someone they're friendly with on the job."

5. She seems restless or irritable at home, especially on weekends. "When a woman has a new romance, she can't help thinking about the other person even when she's at home."