Snowbunny, what did you do before you got to the CR for our wise advice?
Personally, it’s just not your problem. 1, it’s your cousin. 2, he has choices. 3, he’s 30 years old. It’s his problem.
In my humble opinion, your relationship should not deal with it, whether to condemn or condone.
If he behaves inappropriately, that’s another story and you should just avoid him at those times, or, tell him he can’t speak to you like that. Spray him with mace or pepper spray if he treats you badly, that should get through to him. But getting worried about his alcoholism is just not your concern.