You're trying to rationalize and justify his behavior. It may be the drugs, but at the same time understand IT MAY NOT be the drugs. Don't allow the drugs to be his justification.
I understand it's hard to differentiate between being pushed away because of an addiction and plain being told there's not a chance...but you're kind of friendzoning yourself if it's door number two. Are you prepared for that? To invest more time into something that may end up being nothing?
I say preserve your heart instead of adding to the pain.