It's a hard topic, I can understand cheating, I was cheated on 3 times by the same woman, and I don't blame her for doing it, although I do blame her for putting relationships before her son. It's not that I wanted her to stay in a relationship with me for the sake of my son, just every other week she is man hunting.
If you're in a tough situation where you can't get out of a relationship but you want more, I can see how things can lead to people trying their luck. They don't think of it as cheating unless they really examine the situation, often they try to fill a craving or a gap in their life.
But cheating hurts a lot of parties, and I think people should end things before they decide to move on.