I'm so sorry you are going through this. I know what it's like to have your emotions hostage. I would agree with the no contact rule as others have stated. Only because there is truly NOTHING you can do to heal him. One great thing I read above is the acknowledgement that this problem was there well before you, so nothing you do or any action you take, will make it go away. It's as you say, only trying to take you with it. And yes, it does sound like manipulation. No contact will do both of you good. Good for him because it will allow him to truly figure out if he wants to keep down this path as he watches everyone leave, and good for you because it is out of your hands and you know in your heart he is just as capable of getting well as anyone. If he is working, then he is obviously able to get help.
I do send you well wishes though, as addiction is horrible. You feel like you are abandoning them with their awful illness, but it truly is a matter of them doing what they are gonna do, and whether just one or two lives ruined by it. Again, if he is able to work...is he really at death's door, or does he want you to think he is?