First things first - You didn't Cause it, can't Control it and can't Cure it (the 3 Cs).
I don't have any experience with this.
First of all, I know for a fact that I am in no position to ever help someone with their recovery. I have learned a lot about alcoholism, known and know alcoholics and my Father was an alcoholic.
How on earth can I help any of them? I can't, I am not an alcoholic and i'm not a professional. Addiction requires professional help or at the very least the understanding of those that have been there (like AA).
I can't see a place for myself in anyone's addiction recovery.
It actually kind of sounds like you are trying to keep a place holder in this relationship? Trying to think of a way perhaps to keep a foot in the door? Why would you want to do that? You will be purposefully hurting yourself. You just get to ride the same rollercoaster but from a slight distance.
Let's say he sobers up for 2 months, are you then his support and friend? What if he then relapses for 6 months, are you then not his support and friend?
Anyway, I think you are setting yourself up for more hurt. Regardless of what you choose, you at least need some distance after a breakup, say a year at least to think clearly, to detach emotionally, to think about what you want.
Do you want to perhaps be in another relationship at some point? Being a support for your former boyfriend who is a recovering addict doesn't leave a lot of time for your own social life.
The more you focus on yourself, the happier you will be.