I'm Secretly In Love With My Best Friend

I've known my best friend since we were kids, and we've always been close. But over the years, I've started to develop feelings for her. I don't think she knows, and I'm too afraid to tell her. I don't want to risk losing her friendship, but I can't help how I feel. It's hard to watch her date other guys and pretend to be happy for her. I know I should move on, but I can't seem to shake these feelings.