Tony Parker and Eva Longoria. Arnold Schwarzenneger and Maria Shriver. And most recently, Justin Bieber and Selena Gomez (although this hasn't been confirmed). Some men can't stay faithful, even when they're already with gorgeous girls.
Although we don't know the behind-the-scenes details of their relationships, infidelity experts say it's not surprising that guys like the ones mentioned above may be tempted to indulge in sideline action. As it turns out, the reasons guys are unfaithful are rarely about the sex itself, but because cheating fuels a deep psychological need. "Several factors make some men more likely to stray, even if they are dating or married to a beautiful woman," says Don-David Lusterman, PhD, author of Infidelity: A Survival Guide.
What factors come into play
The first factor at work is the man's level of success. Guys in high-profile, powerful positions - such as celebrities, athletes, business executives, and politicians - often have a sense of superiority and entitlement. "These guys have achieved a certain status, and bedding several attractive women further reinforces it in their mind," says Lusterman. Moreover, these men are constantly on the road, away from their girlfriends and wives. At the same time, their prominence attracts a slew of hot chicks who offer no-strings-attached sex. "They may have a wonderful partner waiting at home, but the situation they're in, coupled with their role of pursuer, makes it that much easier to cheat," adds Lusterman.
Related: The telltale signs of a cheat
But celebs aren't the only snakes
Plenty of regular guys are unfaithful too, especially when their backgrounds condone it. Many two-timers come from chauvinistic cultures or families where their fathers cheated. "There are internal blueprints (created by watching our parents) that make cheating more of an option for some guys," according to Dr. Debbie Magids, author of All the Good Ones Aren't Taken. Also, men who were ignored as children often develop deep trust issues, which can make long-term relationships really difficult. "Chronic cheating is rooted in an emotional emptiness that can give people the need to feel constantly desired," she says.
Then there are guys whose bad behavior is actually a mental disorder. Sex addicts, for example, are so enslaved to the rush of sexual activity that they have affairs, visit prostitutes, and consume porn. "Ironically, many of them have happy relationships and feel guilty for cheating, but they can't stop," says Lusterman. Someone with narcissistic personality disorder, on the other hand, can't resist the temptation because he is obsessed with being adored.
Guys who have such extreme compulsions need psychiatric help. But just because a guy fits some of the other categories doesn't mean he'll automatically cheat. "It's important to pay attention to the warning signs, but whether a man will stray or not boils down to his level of honesty within the relationship and his loyalty to you," says Lusterman.
Slideshow: 6 more reasons why people cheat
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