Need relationship help with this girl?

There's a girl i like a lot.. the feelings are gradually fading though.. we used to talk every single day and I'd do anything for her and she knew that. After getting close to her for a few months everything felt perfect, we werent together but she said she had feelings for me and i did for her also. We sure made it seem like we were together the way we talked to each other and stuff..

For some reason we just began to see each other and talk to each other less since a couple months ago.. But before that it was already planned that we'd go to prom together.. She used to be so excited to go with me.. I felt kind of loved and it felt good. My prom was last week and she came with me.. I did my best, picked her up in a great car, tried my best to make her have fun.. Nothing happened between us that night.. NOTHIN at all. She didn't even say thanks to me or even talk to me since then.. When we were close she'd always come talk to me and i dont know whats happened.. What do I do now? Give up? Do you think she lost all the feelings she once had? i dont know.. I just need some INSIGHT please answer