Tell him that if he is really serious about being both of you together and him staying sober, start right now and show that he really meant it - even though both of you have no legal or any disclosure on your relationship. Let him learn first.
When he does, it only means that he is really committed to you and his promises. If not, continue to help him as a close friend. I am sure that one day he will realize what you want him to be and both of your future.