I agree with MacDiddy.
The answer to this question is actually quite simple, best illustrated by a conversation I had with my new brother-in-law the other day about my sister (his wife.)
Him: "Yeah about drugs, blablabla, I mean I like to be honest but.."
Me: "Do whatever you want, just don't get caught"
Him: "Amen, brother."
Once you realize that THE END RESULT is all that matters, and you are smart enough to watch your own ass then cheating doesn't matter.
Cheating is pretty risky because of diseases, the chance of impregnating a girl and other reasons. But, as long as you don't get caught then you're still a good man in my book.
I don't care if my brother-in-law cheats on my sister. But, if he lets my sister find out and go through all the mental anguish associated with that then I'll fvcking kill him.
Likewise, if the situation was reversed and my sister did the opposite I would stop returning her calls because her new husband is a good guy.
The main idea is your life and the results your actions have on your life are a higher priority than morality. Trying to be a hero and sacrificing your own well-being for the sake of morality is for AFC males. Just evaluate whether you really want to cheat with the person when the opportunity arrives and go from there. Make the choice based on reason, not on morality or the societally programmed guilt you may feel.
Just ask yourself, "Do I want to have sex with this person in my lifetime?" If the answer is yes then go for it because the opportunity may not come up again.
Morality is cool, but people (AFC males, especially) sacrifice too much of their lives in the name of it.
You cheated in school because the school system was broken. Take a look around, our social system is broken, too. Don't go around killing people, but don't stifle your desires, either.
And, above all: Don't get caught.