fiancées addictions. help please?

Arianna • With the love of my life and mother to our handsome little boy ❤️
Okay so I'm engaged to my fiancée of 3 and a half years and together we have a beautiful one year old little boy. My fiancées parents are both alcoholics and his mom also is an addict to hardcore prescription drugs. He became addicted to alcohol and drugs at a young age. When we first met he was still on everything and then he went to rehab (for the 3rd time) was on probation and went to jail (violation of probation) and he finally got clean. Once he was completely clean and changed, we decided to start a family together. Now our son is a year old, and he started drinking again. Every single night. He might go a night without alcohol but that's it. He doesn't take any drugs besides tramadol for his back pain because his work requires heavy lifting. I'm going to college full time to become an RN and I'm a stay at home mom while he goes to work and goes to school part time. I have psychology, and learned that our son is most likely to get his alcoholic gene and that chance increases tremendously if our son is around a drinker. I try talking to him all the time and he won't admit he has a problem. He go to couples therapy for other issues and we've talked about this issue as well and our therapist agreed that he had a problem and needs help and suggested AA meetings again. He won't go because he doesn't think it's a problem. I can't help him until he admits it. I don't want our son to ever become like that. I like to think that I'm a great mommy and I'm trying my hardest to give him the best life possible. I'm not leaving my fiancée, I just want to help him get better so we can be happy together as a family. I don't know what else to do. I'm so scared  that our son will become like him if he sees him drinking. Tonight I asked him to not get any alcohol nicely and he said okay. Then tells me he got some liquor. Do I have the right to be mad? When he gets really drunk he gets very mean towards me. Screams and punches doors. Thankfully he's never done that with our son around. He screams at me and tells me I'm a horrible mother because I'm at school so much and I'm not home to take care of our son, my grandma watches him while I go to school 4 days a week for a few hours a day. I see my son before I go to school and spend the rest of the day with him. I take care of him when I'm not at school. I'm the one that wakes up in the middle of the night to feed and change him, and play with him. I do everything. I also do all the housework and never ask him to do anything because even if I did he wouldn't do it. Am I really such a horrible mom? I don't know what else to do. Any advice would be greatly appreciated.