I found this article on Askmen.com and thought it was pretty interesting.
Top 10: Reasons Why Men Cheat
By Oliver Jameson
Adultery has been around forever, and has always given us something to talk about. Most reality TV shows these days center on it, as do gossip mags. But we are far from cracking the big mystery: Why do some men cheat in relationships?
All men know, at some level, that cheating is wrong. From the earliest age, we are taught the virtues of monogamy. "Thou shalt not covet thy neighbor's wife," bellows our Judeo-Christian consciousness. Yet we still do it.
Blame it on the Genes
In troubled relationships, cheating can be an easy alternative to the burden of a breakup or the agony of divorce. It's a quick fix for the sake of the couple's or the family's integrity. Some of us have even gone so far as to enact the long-distance code: If you cheat in another zip code, it doesn't count.
And with evolutionary psychologists telling us that we are wired to lay our seeds in as many women as possible to ensure our genetic survival, adultery is slowly becoming a defensible misdeed, which may explain why women are catching up to men in the game of infidelity.
Because of our insatiable appetite for sex, we men can sometimes only be as faithful as our options. Here are the 10 main reasons why some men will opt to shed their devotion and cheat on their partners.
Number 10
Your lady doesn't put out
Every man has heard that the best way to get a woman to stop having sex with him is by marrying her. Apparently, long-term relationships seem to suck the sex drive out of many women, leaving men gasping for fulfillment. With the need for more sex, some men will start "working late" more often.
Or it could just be that the sex has become boring. She doesn't want to try new things in bed, or won't perform fellatio. Some men may cheat because they don't want their girlfriends or wives to perform certain sex acts that would ruin their "good girl" image, so they get a mistress to take care of it. Like Robert de Niro said in Analyze This , "That's the mouth she kisses my kids good night with!"
In light of this, I call on lawmakers around the world to create an International BJ Day, where men and women get the day off from work and get all the oral satisfaction they need from their partners. I'll bet that this alone would cut infidelity by at least 75%.
Number 9
She cheated on you
So you found out your lady was being unfaithful, and the only way you can relieve your anger is by doing the same. For many men, this is the only way to get back at their cheating girlfriends and even the score. Some men might even cheat to get back at all the cheating women they've had the misfortune of dating throughout their lives; now that's efficiency.
Number 8
It's challenging and exciting
If you consider the women you sleep with "sexual trophies," chances are you have already cheated at least once in your life. Some men simply cannot leave behind the thrill of the hunt, the chase and the conquest. For other men, the excitement is in the variety, like changing ice cream flavors for one day after years of sticking to just one.
Number 7
You can get away with it
"What eyes don't see, the heart doesn't feel," goes the old adage, and it still holds true, as long as there are no cameras around. The knowledge that no one will find out and no one will get hurt is reason enough for some men to grab a different helping. But be careful; as men get craftier with avoiding detection, women get more sophisticated with detecting, not to mention boosting their network of spies.
Number 6
It boosts your ego
Nothing lifts the old self-esteem like discovering that other women still desire you sexually. When in long-term relationships, men may begin to question their sexual marketability, which will lead some of them to sow their clandestine wild oats. Once a man knows he can get back in the game, he'll return to his mate; or not.
What's a guy to do when his girlfriend's-a-naggin' and opportunity comes-a-knockin'?
Number 5
The opportunity was there
It's an uncontested fact that most men can't say "no" to sex. Although guys aren't constantly bombarded with sexual offers, sometimes an irresistible prospect presents itself. Maybe it's a frisky ex-girlfriend, maybe it's a horny hottie on the dance floor. A guy may see it as once-in-a-lifetime occasion that might never be available again. Carpe diem , as they say.
Number 4
Your girlfriend is a nag
Most men have experienced at least one woman who thrives on making him feel like crap. Constant nagging, fighting and squabbling in the right ratios is the best recipe for a headache. Cheating with another woman is a common escape from this domestic hell, and works better than aspirin.
Number 3
Women let us
Truth be told, women are quick to forgive men for their unfaithful behavior. Maybe it's their fear of being alone, or that women are simply the more merciful ones of the human species. Some women might even blame themselves for their men's infidelities, and take steps to improve their relationships. The fact that many women let their men get away with murder might compel them to double deal repeatedly. Just ask Bill Clinton.
Number 2
She doesn't turn you on anymore
Long-term relationships have the annoying habit of making people lazy. No longer concerned with staying fit and attractive, a committed woman might lose the allure she once had. Her man may simply not find her beautiful anymore, and making love to her is not as stirring as it once was. This is why most mistresses are gorgeous, young women.
Number 1
You don't love her anymore
Alas, after a long time together, you have lost the feelings you once had for her. But the relationship has remained too much a part of you. Separating seems so painful, so radical that it's almost inconceivable. So instead of separating, you go elsewhere to get your physical gratification. Most times this does not help matters, but only prolongs the inevitable breakup.
Your Cheating Heart
In the end, cheating is no joking matter. If you are cheating on your girlfriend or wife, it might be that you are unhappy in the relationship, or that you have issues that you should address. Look at the big picture and see your unfaithfulness as a symptom of a bigger problem.
Cheating might feel good as a quick escape from your problems, but it's only an anesthetic -- not a long-term solution.
Doc
Which is extremely immature and I think reflects their own inadequacy and probably negative feelings about themselves that they have to boost their ego by having more than one partner at a time and thinking they are so smooth. 
