Most Helpful Guy
You're correct. It doesn't matter if she slept with him or not, the point is that she went to her ex's aid and spent the night with him. That is a no-no. I can't believe the disrespect you let her treat you with. That is a major red flag. You should've put your foot down when she even brought that up. Don't ask your girlfriend politely to disregard her ex, you should be taking it as, "If you go over there, this relationship is over. I don't put up with that kind of disrespect." She clearly still has feelings for her ex, I'm sorry man. You have to do what's right and what's HEALTHY for you now and break it off with this girl. I guarantee you will have issues with her later if you continue this relationship. You let her disrespect you. You showed her that you have no backbone and you let her walk over you like a doormat. To avoid being used and abused you should've been more like "WTF?" and completely questioned her about why she's going over to see her ex, if she still insisted that's when you show her the door and say bye, have a nice life.
Now, you can still respect yourself right now and move on with your life. You should be living your life accordingly to what's best for you, not what's best or "fun" for her. You showed her that it's OK to disrespect you, don't disrespect yourself by allowing that. Be a man, stand up for yourself like you're talking about. I believe in you man. Life is what you make it, do what's best for you, not what's best for her.