I think i'm infatuated with my English teacher and i don't understand why...?

He's about 17 years older than me (I'm only 15) but he doesn't even look like he's in his 30's at all. the first day back in frosh year i thought he was a senior or something imagine my surprise. Ever since last year i can't seem to stop thinking about him. i think its more of a physical attraction than anything else. Its just i cant seem to stop and the fact that i see him all the time now isn't helping either. And he's not even the gorgeous type he's more of the always serious looking quiet one.