Don't beat yourself up over what is going on with him, the best thing to do is talk to him. Let him know you like him, if you think that he thinks you are a narc, then just be more subtle, ask him if he wants to grab something to eat with him or a movie on friday night, maybe you guys could smoke after the movie, who knows. But if he was excited at first, chances are he still likes you.

Trying to figure out what his deal is would drive you crazy, and probably not even worth worrying about. But if you do like him, which it seems, then just ask him out on a date first, let the pot come after