Hi Mambo I know the sages will be over here soon, meanwhile I will offer my humble 2 cents.
You are not "the only person" who can save him or not... he has to save himself through reaching out to others and there are so many ways, he has family, I am sure he knows where to go to an AA meeting, counselors, doctors, helplines, 911, past contacts while he was doing well etc etc ... just like you have realized where and when you needed help, reached out and got it... he can do exactly the same.
It is not like he is a dying stranger and you are ignoring him... he has had a lot of chances to choose better...and at one moment he had all your love and understanding. He had all his sisters' love and understanding. What has he done with all that support? He has made sure everyone who came close and cared, left, like you, not without much pain and guilt.
I say leave him at the hands of God/HP. You can't control someone's life, only yours. It sounds cold but this is not an innocent suffering, he is where he is at by a long string of bad choices, and here they are - always in a timely manner - the consequences.
His life or death is not up to you. If he can call you he can call anyone else. You cannot cure it Mambo queen. He has to want to cure himself, and want it more than anything else. Then and only then will things turn. That is between him and God/HP. It has nothing to do with you.
I send you strength and hugs... it is so easy to talk, it should be really tough ((Mambo queen))