3 Months? You've been dating him for 3 months, he didn't even tell you he was an addict for the first month, and you're choosing to put yourself through THIS? And your fear is that he might find someone else if he does the recovery thing?
My own philosophy is that dating is like interviewing. You have the right to say "sorry, not a match" at any time for the first few months -- But then again, maybe you need a project, and being with a guy like this fulfills that need for you.
I'm not doing so well with the advice thing here, but I guess I can't quite figure out what it is that you want.