Honest advice:
Don't believe anything anyone tells you, in a relationship there will always be people that don't want you two together, or like the girl themselves.
If you still love her then show her that, and your confidence should have never been gone, if she didn't like you, she would have broken up with you.
Your best bet is to just ask her "what's wrong, has anything been bothering you lately?", if she says I don't know or No, just tell her you really want to help and she should tell you.
I hope everything ends well for you!