That's actually happened to me only one time before, and I spent the majority of my high school years trying to pretend my feelings for her were nothing more than just those between friends - I'm sure it was more transparent than glass. Even so, I always figured she was just ignoring my advances, and that was that. Only later would she tell me that she had the same feelings for me the whole time, but never acted on 'em. Oh, and by later, I mean three days before I moved off to college. :|
Still, I've been on the other side of the looking glass as well. I'm pretty introverted, and it takes me a while to develop feelings for people beyond the friendship level. That being said, my more outgoing friends made advances on me I just had to shy away from. I mean, if the feelings aren't there, they're just not there, right?