Boyfriends drinking DESPERATELY NEED HELP?

My boyfriend drinks around a 5th of cheep vodka every single night alot of times more. This is really starting to take a toll on his health i can tell because his skin and his eyes are looking so dead and he always breaks out in rashes everyday he looks like hes closer and closer to death and he doesn't even realize it I am so worried for his health. Before I could tell his health was being effected he would just get mean and violent when he was drunk sometimes. The only fights we've ever got in have been when he was drunk. I love him so much. I just want him not drink but every time i try to talk to him about it he gets mad and yells at me and accuses me of trying to control him..I was going to write him a letter and leave it at home so he gets it when hes out of work. But I'm not sure what i could say to get him to understand. I want this for him not for me. please help..