It's natural to feel that way. I had a crush on a girl took with me a couple of classes in my undergrad studies, and I think she liked me because she once came and talked to me and took my notebook to copy it, beside all the looks she was giving me. I was afraid to talk to her. So, I let it go, and I regret it, because to this day, after 13 years, I still dream of her, and even search for her on the Internet (but to no avail). Probably she is married and have children already, anyway.