I think it is very common for girls at your age to have a crush on mature male teachers. I did this several times and am still having the problem.
I myself is a part-time teacher, and I guess teachers are really good actors and actresses (someone mentioned it before me). I don't know why you've had such a crush. For me, that's because they are mature, elegant, knowledgeable and because we see each other every day. Young girls tend to have crush on male figures around them. But the elegance and the maturity they have may be only acted out, i.e. in real life they might be very dirty, very childlike, very lazy.
I was not saying the teacher is not worth your attention, but that you need to know more about him before you can decide whether to further the relationship or not.