Why is there a tendency that a person cheat their partner?

Cheating has been human's way of rejecting a person or selective as it has been part of humans survival instinct from times immemorial. Cheating a girl friend or boy friend is just a part of selection process we have. Of course it stems from greed one has on other material things like money,.. which makes one to reject another.

I tend to hide some things which I am not comfortable with my wife but one fine day I was caught red handed. Most of the things will be financial things or some health related problems. I used to eye on other gorgeous girls but could not due to my limitations. I want to cheat but not dare to as it requires a lot of risk to which I am not ready at this point of time.

hello chiltacs,
For me, I think they're not really compatible to each other. But, he should tell to her that he doesn't love her anymore better than cheating on her. Or maybe, they need to talk about it so they can adjust and change that is if they still love each other.
There's a lot of possibilities when one of the partner will tend to cheat. That he/she does not really love her/him. That he/she just want to try. Want to prove that he is a man. When one of them got bored or tired to something. Whatever the reason is, it's not fair.