It is horrible to know that something can have such a power over a person, that they are willing to throw everything away.
Your AH is in a really dark place. Remember that it is no fault of yours, it is no flaw in your character, it is not because you didn't try, didn't care. Remember too that it is not because what you did for him was not good enough that he is unable to recipricate when you are down and out. It is because he is completely controlled by his addiction right now. If he can come to another moment of clarity, perhaps he can navigate back into the light, but you nor anyone else can get him there if he doesn't choose to go.