Search Results: girlfriend sleeps around on me

So I and my girlfriend fought over this issue. I need you guys to tell me who is right. My girlfriend went to a guys house at night to see a horror movie that was 1 and a half hours long but they ended up watching it for 4 hours because she was drunk and interupting in between. He put his arm around her and watched the last half an hour of movie. And then both of them slept in one bed. According to her they on opposite sides of the bed. All this happened when we were in a relationship. She doesn't feel guilty about it. The point is Is it right to go to someones house drunk and spend a full night alone with that guy and watch a movie for 4 hours while a guy has put his arm around you and he is not his boyfriend but she has a boyfriend? Was she did was ok or not.
Kindly give reasons for the answer you chose.

Admittedly have acted flirty around other girls when I was in a relationship. I remember one girl wanting to sleep with me but I told her no. But there was some hugging and caressing (no kissing). I felt semi guilty about it but I didn’t cross the line.

My girlfriend at the time never questioned me and trusted me 100 percent. But down the road she was pissed off at me for different reasons. I’m almost completely sure outright cheated (slept with another guy) a week or two before we broke up. I just could tell from her body language something happened. But I never got it confirmed.

But anyway is acting flirty around the opposite sex cheating when you are in a relationship cheating?