It also appears that money doesn’t buy marital happiness. For men with money, infidelity is just another perk. Among men making more than $300,000 a year, 32 percent report cheating, compared to 21 percent of men making less than $35,000 a year. Wealth isn't much of a factor in women's cheating.

“Wealthy men may simply have more dating opportunities than men with less income,” says David Frederick, a psychologist at the University of California, Los Angeles, who helped analyze the survey findings.

'I like variety'
What drives people to cheat? Boredom? The thrill of the forbidden?

Many thrive on the excitement they get from a fling (30 percent overall), but men and women are generally prowling for different things. Men want more sex (44 percent), more satisfying sex (38 percent) and variety (40 percent), findings that closely resemble the 2006 MSNBC.com/Elle magazine survey on monogamy.

“Mostly I’ve cheated because of the excitement,” writes a 38-year-old man who took the survey. “I like variety and a more wild sex life than I’ve been able to enjoy with relationship partners."

Women's motives range from the need for more emotional attention (40 percent) to being reassured of their desirability (33 percent) or falling in love with someone else (20 percent).

While women tend to cheat once, guys of all ages are twice as likely to be serial offenders.

“Men are more likely to look for sexual novelty. They might be looking for a sexual outlet without the expectation of continuity,” says Sandra Leiblum, director of the Center for Sexual and Relational Health at the Robert Wood Johnson Medical School in Piscataway, N.J., who was not involved in the survey. “And once you satisfy the itch, it recurs.”

A gender split between sexual and emotional drivers can also be seen in attitudes toward wandering partners. Women say they would be more upset if their partner fell in love with someone else than if their partner had sex with that person (65 percent, compared to 47 percent of men), but men say they’d be more distressed by their partner having a sexual affair than falling in love (53 percent, compared to 35 percent of women).

Survey results are in! Who's cheating and why All the juicy details: Infidelity by the numbers To stay or stray? A crime of opportunity Survey: Influenced by cheating celebs? Is virtual affair real-world infidelity? Readers respond to the findings Loads more on infidelity from iVillage.com

“Men are more threatened sexually by the sense of competition and comparison; women are more threatened by the loss of the emotional intimacy,” says Leiblum. “Whenever there is an affair there’s a sense of competitiveness with the third party. Men see it as a comment on their sexual competency and masculinity, whereas for women it’s not the sex, it’s the meaning of having the emotional bond with someone else.”

It's not all about mushiness for ladies — one in five who cheated said they were looking for more satisfying sex than they were getting from their primary partner.

“I was miserable in my marriage of nine years,” writes a 28-year-old woman who ended up divorcing her husband to be with her affair partner. “My husband and I never had sex and the sex we did have was boring!”

Women are also twice as likely to use an affair to get out of a bad relationship.

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