GF Cheated on me while on holiday :-( I'm complete mess

Been together for 6 months, had our ups and down but really liked each other. She went for holiday for 2 weeks. Once she was back, we were doing all sorts of activities like climbing, walking and going to different places. But she got absolutely drunk and slept with her male friend's friend. She still hasn't told me that yet, but we have a mutual good friend and my GF told her about it, and that she wasn't sure whether to tell me or not, but would def break up with me. What should I do? I didn't sleep last night at all. I feel like throwing up all the time. I've been replying to her messages normal but with a delay. I did have thoughts of cheating on her recently because she wasn't very affectionate, but doubt I'd have cheated on her though. Now, I'm a complete mess - what should I do? I can't see doing things without her. I can't see myself going to the place we went and not having her holding my hands. I can't see not getting to spoon her. But I can't trust her anymore either. Can being drunk ever be an excuse for cheating? Please please say something to help me out, I'm a complete mess right now :-(

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