What do I do if I love my best friend but she has a boyfriend?

My best friend is this girl who as soon as I saw her I knew I loved her! And it was platonic for a while but then she got way into me and said she over me and all this stuff and then she got a bf and now it's really akward cuz she knows I still love her and I don't know what to do!! But I love her more than anybody in the world!! (oh yeah,and she's bi-polar) I'm fourteen what do I do???