Wow, it's interesting how black and white this issue is for a lot of people. She's a slut, cheaters have no morals, etc. I guess that even though I believe cheating is wrong I think there are many shades of gray. It's easy to sit back when you're not in a situation and judge it...
In my marriage we both feel cheating is a breaking point. But then, it has never happened so my opinion on it comes only from what I think I would feel or do. I know couples who have survived cheating, and they must have had reasons to keep going or they would have ended things.
However, I still think that if I cheated on my husband, the fault would be mine. Not the man I cheated with. He didn't make any marriage vows to my husband, I did. Whatever issues the man may have, I would be solely responsible for the my own actions which would hurt my husband and/or destroy my marriage. The blame would not be 50/50. As I said, opportunities and temptation will always be there, to think otherwise is foolish. Remaining faithful and honest is a choice.