Men almost never cheat because sex. Maybe about 8% of the time. Normally it happens because of some profound unmet needs. Statistically, it doesn't happen as much as you think either. (Somewhere between 20% and 37% of men according to most studies I've read. Far from the 99% that the media wants you to believe!) More often men are going to stay faithful in their marriages and be miserable for as long as they can take it. When it does happen, it's not usually a "sex" thing. He's starving for something else.
A starving man is either going to steal or die...and given his instincts to live, he's probably going to try stealing first.
The men who read my blog and belong to my Facebook page have begged me to address this issue, but I've avoided it for a long time because so many of my women readers think it's excuse-making. However, one thing I've learned about relationships is that problems within them are rarely one-sided. Rarely. Not saying it doesn't happen and neither am I blaming the "victims" but a lot of adultery in marriage fits into this category. Very few cases of infidelity involve a woman and man who were actively meeting one another's needs and one person just decided to stray out of the blue!
If you starve a person of a major need, after a while they are going to seek it out or die. A man's need for respect and admiration will often contribute to him looking for it wherever he can find it - even if in the company of another woman. This is why we (the public) are often shocked at how "plain" some of the mistresses of prominent men look. We wonder to ourselves "Her? Really? He was willing to risk so much for her!?" Where, in reality, often that woman has learned how to stroke that man's ego in some ways he was sorely needing.
Does this excuse predatory and irresponsible behaviors? Not at all. Remember, however, that we're talking about needs. And needs, by definition, must be met and there are countless men who are facing a few demoralizing choices even today as you read this: commit adultery, end the marriage or die.
Needs must be met. A skillful woman learns how to address to address this need at home.