Time to let go.
His recovery is his problem. He apparently, for WHATEVER reason (and it really isn't relevant for your purposes), is not ready for a relationship with you. Period.
Forget about the addiction for a moment. Suppose he had simply left you, with no explanation, in other circumstances. You would still have to grieve the relationship and move on. Analyzing why, why he is behaving this way, does nothing for you.
Focus on your own healing, and let him worry about his.