Why doesn't he want to date me? (I promise that's less conceited than it sounds)?

Honestly, it's probably because he's afraid that if something happened in a committed relationship, it would tear you two apart, whether you think so or not. This is especially true if he has been hurt in previous relationships. It's not that he's not totally interested in you, he's just trying to stay at the best level he can with no potential risks. I think that in time, things could change for sure, but only after a significant amount of more time. I know that this isn't what you want to hear, but cherish what you have with him, because in some ways you kind of are dating him, just not physically.