I'd take him aside and say that it's really none of his business that you smoke, and that you appreciate the fact that he cares about you a lot and the descisions that you make, and that's cool I guess, but true friends shouldn't really be trying to judge, they should just like you the way that you are and accept you, because you are your own person, see what I mean? I dunno.. that's kinda a tough situation.. do you really want to still be friends with him?