To Fulfill His Biology:
You know the old anthropological tale. A man's main job, besides killing the saber-tooth, is to spread his seed in order to ensure the survival of his genetic legacy. It's a man's biology to want to wander. Does that mean he should, or that he can't help it? Of course not. But it does mean that a man is going to have strong-extremely strong-biological urges to knock on the doors of neighboring huts. I have had this argument/discussion/conversation with dozens of men and women: Are men predestined to cheat? My answer is no, they're not-despite their biology. But often times, they do have to fight it. Especially after a pitcher and two shots of Jack.
To Get the Attention:
News flash: Sure, some guys cheat because, well, maybe the sexual frequency has slowed a bit, and maybe hot-and-heavy happens at home about as often as Rob Schneider gets nominated for an Oscar. But the truth is that plenty of men who are having regular sex with their partner are also having sex with someone else. Why? Because cheating isn't just about the sex. Just as a woman who cheats may be seeking more affection than what she's getting at home, a man often cheats because he's seeking the attention that he no longer gets at home. Part of the allure of the mysterious woman isn't just to find out what she looks like naked; it's that the woman showers the man with flirtations, with seduction, with advances that make him feel like he's worthy of more than just fixing dents in the drywall.
To Get Out:
I know lots of guys who simply don't have the strength to end it. They may try ("I'm just not happy"), or they may take other tactics to drive a woman away. A lot of guys simply have trouble breaking off relationships because they don't want to be perceived as that bad guy, the jerk, the insensitive lout who ended something good. So they tiptoe around the issue in hopes that she'll get so frustrated that she'll back out first. Well, if that doesn't work, then a man knows that the only way out is to commit the relationship sin that drives a woman away for good. It's not right, but it's what happens.
To Change Up His Play List:
Think about what's on your iPod. You have your favorite songs you play over and over, but every once in a while, you're in the mood to hear something you haven't played in a long time. You don't need to hear it but once every month or so, but still, you appreciate the changeup. Relationships need to be like good iPods lists. You're comfortable with your routine and you like your routine, but it's always nice to change things up. What men really want in relationships (and what I suspect women also want) is to be able to take comfort in the routine of a long-term commitment, as long as there are some surprises that make it feel like a new relationship every once in a while. In order to keep the relationship strong, you've got to change the songs every once in a while. That goes for in the bedroom and out.
Taken from somewhere. Credit goes to original writter.