Addiction destroys everyone and everything in its path- doesn't discriminate between anyone no matter how hard the person tries to help the other. or whether the person doesn't support the person at all.
Do not feel bad about not "supporting" him enough. You are not selfish, HE is the selfish one. The book mentioned above really helped me and I also read "Codependency for Dummies" actually really opened my eyes through the examples it provided.
I also agree that if someone threatens to hurt themselves or others it is best to call the police. You cannot control what someone says or does, but you can take actions to protect yourself. Also once you call the police then it is easier to see that it is not your fault, you can't control it, and you can't cure him. I am a HUGE advocate of counseling, I truly feel that it gave me healthy tools for dealing with anything has come into my live. I treasure that time I have with my therapist, I actually look forward to my appointments. Meetings will also provide you with support from those that know what you are going through, and sometimes it helps to have people face to face to talk to. Can you lean on family a little bit too? Family has been a big part of becoming healthy for me.
Be kind to yourself, you aren't able to change him, but you CAN take care of yourself.
HUGS