Here's the thing on this....
When someone chooses to "cheat" they are making a decision to break a trust. This is a decision, that anyway you cut it, is totally selfish. I don't care what else may or may not be going on within a marriage, choosing to cheat is a totally self-centered endeavor. It is not about anyone else but you (universally speaking

). The person to whom you are supposedly committed gets a raw deal, and the one with whom you are cheating gets someone who isn't free to, can't, won't, has no desire, is incapable of (take your pick or add something new) giving more than a very limited, compromised relationship. In any case, the primary person is the only one really winning - if you want to call it that- which I wouldn't. There are always other choices.
Marriage is hard work, and sometimes that grass may look greener. However, one must be careful...sometimes that beautiful, green grass is planted over a septic tank.

I know that many celebrities have people throwing themselves at them all the time. This would be difficult, however, one can always walk away, or not put themselves in a position to be compromised in the first place.