<human>: Can you condense the text into a few key points?

So this happened a few days ago. I have been dating this really hot girl for a few months now, we didn't had any sex all this time because she said she wanted to get comfortable with me. I did really like her so I ran with the idea anyways fast forward to last weekend when I brought her to our flat (sharing with my brother). My brother and I are very open to each other like best friends so he knew the gist and he have a gf for the last 4 years. We all got to drinking and got pretty fucked and I realised that she was flirting with him , I ignored it assuming its the alcohol. 

Next morning she is trying to break up with me because apparently she finds him more attractive. I got really mad and I told her off and broke up with her instead. I told his to my brother and asked him if he would shag her as-well to which he got really mad. He said he would never do such an awful thing to me and now I feel like I didn't handle the situation well.
<bot>: TIFU by telling by brother my ex finds him attractive and he got mad because how could I even think he would do such a thing to me