Advice needed about dealing with being cheated on
I have been going out with my boyfriend for a year and a half and when he is sober everything is honestly perfect, but when he is drunk can be very self destructive, getting to the point of incapacitating himself, and sometimes saying really horrible things to me that he would never say when sober. It has been the only thing we ever fought about, and he told me he would go see counselling about it in earlier this year after a fight we had, but, right after that, his dad passed away and he never went because he was dealing with that instead, which I think was understandable.
Last week, he got really drunk and slept with another girl I live with who he is good friends with.
I know that he would never do anything like this if he was sober, and he has told me it is the biggest mistake he is ever made and he can't believe he has thrown everything we had away. I also knew that they were attracted to each other but I never minded because I think it is normal to be attracted to other people even when you're in a loving relationship and I don't think it's an issue as long as you know not to act on it.
I don't know how to deal with this as I live with both of them and see them every day, and I am going to a music festival with the two of them and a couple other friends in a month's time. I wish I could take him back but i know that I can't, at least not until he takes steps to address the issues he has with drinking.
I'm also finding it hard to be angry with him because I know that he is not a bad person and that this is not who he is.
What should I do?>