I can see that you're drifting apart and it's worth seeing if the friendship is something you can repair. It's tough though when she's done some things that you don't agree with and hasn't been the best friend to you that recently. See what happens and try to be open-minded. Why is she drinking so much and hooking up with random guys? There might be a deeper issue under the surface that she's been holding back. This is the time where she needs her best friend the most but if she keeps putting you in uncomfortable situations and doesn't attempt to fix them then maybe it'll be time to wonder if this friendship is good for either one of you. See what happens though. Perhaps things may work out.