I like my best friend's crush-what do I do?

It sounds like you made your choice a long time ago, and I applaud you for it. If the guy was worth anything, he would have tried harder to get you. It sounds like he's moved on, because he didn't like the effort. Your friend is worth more than him! You're not guilty for liking him, that's not something you can help. You should be proud of yourself for being honest with your friend, and choosing her friendship over your crush. Tell her that you value her much more than him, and that's why you never acted on your crush. Tell yourself that if he was worth it, he would have worked for you! You and your friend can feel free to gaze on him from afar, but know that acting on it would never be worth it.