Cheaters

I don't know if you read this article by David Zinczenko but I found it very interesting. He quotes several studies that have found common traits in men that cheat. To sum it up for you, these are the signs as quoted in the article:
"Cheating Sign #1: He Doesn't Pay His Bills On Time

"Some research shows that unreliability and carelessness is part of a personality trait called "low consciousness," which is a marker for infidelity. Makes sense. A guy who's careless about his own responsibilities is going to be just as careless about his relationships."

Cheating Sign #2: He's A Do-Gooder
--to summarize: He goes over board doing good to salve his conscience.

Cheating Sign #3: He's Rolling In The Dough
--to summarize: If he is independently wealthy, he feels less of a need for a partner

Cheating Sign #4: He's A Yeller

"While yelling and anger may not seem to be all that connected to cheating, a recent Australian study found that unfaithful partners show many of the same personality characteristics as abusive ones. Those who are more likely to be abusive (verbally or physically) are simply more likely to be unfaithful. What's already bad has the potential of getting even worse."

Cheating Sign #5: He's A Mirror Hog
--To sum it up:
This one is obvious, he is self absorbed, and doesn't think about how his actions hurt his partner.

"And, yes, this works both ways, as Men's Health explained in "6 Signs She's Ready to Stray."