Originally Posted by JinnKai

Absolutely! They're totally different.

When two people enter into an "agreement" like an exclusive relationship, only those two parties are responsible for maintaining that agreement. She agreed to be monogamous with him, not you.

I've said it a million times here and I'll probably say it a million times more - if my girlfriend cheats on me with another man, I have nothing against the other man. After all, he didn't agree to be with me, she did. If SHE breaks the rules, then it is HER fault, not his.

If you cheat on your girlfriend, then yes, you're responsible. Because, once again, you're the one in the agreement. Not the third party.

Think of it this way; did you meet this guy, hang out with him for a long time and then agree with him that you wouldn't sleep with this girl? Or did she meet the guy, hang out with him for a long time, and then agree not to sleep with other people? The person breaking the agreement is obvious.