Attracted To A Teacher. Can't Get Him Off My Mind.?

I'm obviously not in school right now, but I can't quite shake these feelings.. I'm 17 years old and the teacher is 29. He was one of my science teachers and science is definitely not one of my specialties, but there was just something about him.. The way he talked and moved around and his personality just made me extremely attracted to him.. but there is something else I can't wrap my fingers around... In all honesty, I feel terrible about feelings this way. I have a boyfriend whom I've been with for three years and I love very much but I can't stop thinking about this teacher. I mean, I have another teacher who is also very attractive and more of my personality type, yet the other teacher I feel some sort of strange attraction beyond just simple lust. What should I do to shake these feelings or should I act on them? I use to feel very awkward in that cl. He use to stand near me when he spoke and I caught him looking at me while I was turned away. I will be 18 in two months and graduated midterm so it isn't impossible to act upon. I can't believe I'm thinking like this, but what should I do? I can't help how I feel.