Feelings of loneliness seeing an old crush

There was this first college crush of mine who was very much into geeky stuff but turns out she was very antisocial and never ever talked too much with me. She had a boyfriend when I once asked her out. It has been an year since. I don't want to be with her but somehow her presence in my class makes me very uncomfortably melancholy. I want to forget. Yet, the class' atmosphere is such that there is not much connection and fraternity among anyone. I feel terribly lonely when I see her.