My brother kissed my babe

Good day house, please I need your help with this. I am a twin, my brother and I are identical twins. We were at a friends 27th birthday party so we had all had a few to drink but I wouldn’t say any of us were drunk. Half way through the night I hadn’t seen my girlfriend for a while so I went looking and found her with my brother down the staircase of the house. They were kissing, his pants were undone and her skirt was around her waist. We all got into a big fight and our friends had to separate us. My girlfriend was tipsy at the time and had since sworn she thought it was me, she has even threatened to press charges against him. I am working through this, if she really was assaulted she deserves my support. For his part my brother swears he was too drunk (I don’t believe he was that drunk) and that she approached him. My girlfriend agrees that is true she approached him but that she thought it was me. What makes me believe her over him is that he changed his t-shirt to an almost identical one to what I was wearing at some stage during the night (I hadn’t seen this). Some of the others there say they thought he was me as well so it wasn’t just my girlfriend who was fooled. Anyway what makes things difficult is that we still live at home and have bedrooms next to each other. My girlfriend wants to press charges and get a restraining order against him. It has thrown my whole family into chaos. I don’t think my parents are handling it well at all and dad wants to throw him out of the house. Mom keeps questioning me about whether I can be sure about what my gf has said. She has even questioned her herself when she came over one day and I wasn’t home yet. My ex has contacted me and said she was propositioned by my brother when we were together but she laughed it off and never bother telling me. Since then she and my girlfriend have become pretty close. It is really awkward as my ex and I didn’t split on good terms. It’s all just a mess. I am moving out with my girlfriend would be a start and then we could focus on just us for a while but we don’t have the financial capacity to do that. I have so many questions, why being the obvious one. But more than that how, if it’s even possible, can all these various relationships be healed? I am talking my parents/brother, me/brother, my gf/brother. I have been with my girlfriend for about 9 months and for the first time in my life I feel content, I do believe she might just be the one. I didn’t really ask many questions did I? I’m just lost as to what to do. My support lays firmly and firstly with my gf but apart from that I don’t know what else to do. This all happened about 6 weeks ago and I have barely spoken a word to him since other than to ask him to apologize. He refuses swearing it was her. I would appreciate any advice