Need help ending a friendship

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My sister introduced me to a guy because I was new at a college I was transferring to and didn't know anyone. He was a freshman when I started. At first everything was really fun and we had a few things in common. I then made the mistake of letting him drink with me. He has over time began to show a lot of emotional and maturity issues over time as I have gotten close to him. About four months in our friendship he would constantly talk about killing himself or his roommate because his roommate had a girlfriend and he didn't. I had to take a lot of time out of school to appease his emotional needs. Then he eventually dated a meth head... A few weeks later he attacked his roommate and went to jail. He ended up not getting charges pressed against him, but has to do some type of parole thing to get it wiped from his record. He has a few friends in his shitty fraternity now, but as a result he has become an alcoholic and keeps trying to "hang out" with me just so I can buy him alcohol. He can't even carry on a conversation with me without getting plastered drunk. The last time I was with him he got very violent and started vomiting everywhere because he was so drunk. I had to watch him till 4 am so he didn't choke on his vomit. After this I just see his life spiraling downward and I don't want to go down with him. He texts me frequently to hang out and I have come up with excuses to stay away from him. All he wants me for is alcohol because he is too young to get it. My biggest worry is that he knows where I live. He also knows my girlfriend and they are friends on social media. I don't want him to come to my house and try to attack me. I also don't want him to make a bunch of stuff up and try to end my relationship. He seems like the type of person to do it too. I would have never have even spoken to him if I knew he was so self destructive. How can I get him to leave me alone without having him do something drastic?

TL;DR: My friend has become a violent alcoholic.