Toxic family members

So my SO and I have been together for a year. In the beginning, he was super close with his cousin (as he has always been.) I did not mind it at first, but then I started noticing that his cousin was trying to “hook up my bf” with other girls. He is a consistant drug user. Through all of this I still said nothing because he was my SO’s cousin. There were times I had to walk home from work because my SO had my car and was getting fucked up with said cousin. Through time I eventually had enough and I said I didn’t want that cousin in our lives. In October, my SO had a relapse and it hit me really hard. We broke up and I started talking to another guy/sending pics. My SO came back I forgave him we moved on. His cousin eventually found out what I did, kept it a secret. On Christmas, we all got together and my SO was getting drunk, I didn’t mind to an extent. Then I said okay you have had enough. His cousin got mad and randomly asked why he was blocked. I explained why in the nicest possible way. He then took my boyfriend away and showed him my pictures. My boyfriend was so drunk he dumped me on the side of the road in the freezing cold and left me to go relapse with said cousin AGAIN. New Year’s Day I found out I was pregnant. Yesterday, my SO was keeping his phone away from me and I finally saw it and it was because he was talking to that cousin AGAIN. I don’t know what to do anymore and it breaks my heart because my SO has a large part in this. But he now refuses to stop talking to his cousin and I told him I dont want that cousin in my life or my babies life. I just don’t know what to do 😭😭😭