AHH, can't sleep because I can only think about her (help me please)?

A few weeks ago something happened between me and this girl I'm friends with (I've been secretly in love with her for years but was able to suppress it until recently). Anyway, I decided that I wouldn't talk to her anymore, and she hasn't made any attempt to contact me. And I was decently ok for the last few weeks (well I still thought of her once in a while but it didn't bother me that much, I guess it didn't sink in). But yesterday one of our mutual friends was pestering me about what happened between us and now I can't stop thinking of her. I couldn't sleep last night, I don't know what to do. She has a bf so I can't just come out and say how I feel about her (they've been dating about 6 months and it's always bugged me but I'm really starting to hate the guy). Any advice?