I don't know what to do

Let me just go out and say I posted on another reddit community and I realized it was meant for life after narcissism so I apologize for that I didn't fully notice the name of the subreddit. I just wanted to ask this and give a more detailed story on this as well. So my cousin does certain things that makes me feel like he is a narcissist. First everything has to be his way or he never wants to do it like if we want to watch a movie we picked he says no and picks his movie instead stuff like that and he always has to call the shots. He forces people into things and when they do not want to do it, he guilt trips them like one time his girlfriend did not want to play a game with him and he said that if she loved him she would sacrifice her happiness for him, when he doesn't get his way he gets angry easily and then yells at the person and when you try and explain he just leaves the conversation and never hears the other side of it. He can never be wrong and if he is he tries and justifies it and blames someone else for it. It got to the point now where I notice this stuff more and more like if I do not like a movie he picks even when I watch it he accuses me of not trying new things because I do not like it but if I try and ask him to try something new he doesn't try it and criticizes it. He makes rude comments towards me and his girlfriends interests a lot and doesn't fully talk to us that much anymore as well and when he does its always his stuff not ours. His girlfriend was sad one day he asked what was wrong and instead of being supportive he just sat on his phone while she explained everything to him and said he wasn't paying attention and when she explained it again he just called her stupid. Today he was trying to force me to play a game with him and I said no I'm good and his girlfriend backed me up and said no as well he then throws a fit and accuses us of double teaming him and says we complain to much and tries to make us feel bad. His girlfriend calls him out on it and says he just told us to get on and never asked us our day or if we wanted to he just told us to get on. He then leaves and after that I just do not want to hang out with him anymore to be honest like if he acts like that all the time it hurts but I just do not know what to do. Any advice? Also again I do apologize for telling this on another subreddit meant for something else I did not fully read the community PSA so I just wanted to apologize for that.