I (25 M) and my girlfriend (45F) are crumbling

This entire relationship is so complicated that it would take a novel to explain the ins and outs of how it came to be. She was a family friend first. It didn’t have a good beginning and it cost me my family (parents, siblings) by getting with her, as it probably should have looking back on it now. But anyway. Some things happened that cause distrust for me. Things that happened before we ever really got together. I can’t prove it beyond reasonable doubt. But before I lost contact with my family, I heard from the people that it supposedly happened with that she may have done sexual stuff with some members of my family but she swears on the lives of her children that it didn’t happen. But I just wanted to trust her as our relationship started to slowly blossom. We started hanging out a lot at her friends house. In the beginning, her and her friend drank a lot together. Dancing, partying, etc. Which isn’t necessarily a problem but it is NOT my style at all. As our relationship started blossoming more she started taking me around their kids more and the whole thing has just gotten more serious and I’m basically the stepfather of her 2 kids. The longer we were together, the more I voiced my dislike for the drinking and partying. It kept happening. I started begging “please don’t drink too much tonight” and she would become belligerent and we would fight. The cycle would repeat. She started promising me she wouldn’t drink over there or at least as much over there with her friend. I would look over and see her sneaking shots and you better believe if I said something, I was getting fussed at. We went on a trip with this friend and her family that went HORRIBLY. Everyone was drunk basically the entire trip. They all knew my feelings about drinking and how it wasn’t my thing and how I’ve been through some tough times with alcoholics in the past. They begged me to come join them and I had finally had enough and told them how I have had enough with the drunken antics. How I’m tired of how they influence my girlfriend to drink and how it just ruins everything. At this point I was balling I was so emotional. Her friend grabbed my hands and looked me in my eye and said “I understand exactly where you’re coming from, I know you’ve been through a lot, etc. I promise you that tomorrow, we will have a sober day and everything will be great!” Well…the next day, they drank more than they had the days previously. So much in fact that the cops were called because her friend was acting a fool at a Taco Bell and I had to go pick her and my girlfriend up before they got there. Anyway, I’m basically at my wits end with this friend and her husband. I can’t stand to hear her name. I am DONE. And I tell my girlfriend that if she wants a healthy relationship with me, she basically needs to cut this friendship off. I know it’s an ultimatum and that you shouldn’t do that but I’m being driven insane. My girlfriend says I’m abusive, that I’m ruining everything, that I’m just like members of my family who abused me, etc. I can’t be in a relationship with her if she’s friend with this person. I’m so frustrated. Is there anything I can do to improve this situation?