Crushing on my BEST friends brother?

Well, from what you said about your friend not supporting your decision, she doesn't sound at all like what a friend should be if she is your BEST friend she should respect your feelings. You should tell him FIRST and you two can decide what to do together. Don't be afraid to show your feelings just because your nervous about how your "friend" reacts. I liked one of my friends brother before but she was fine with it, she made fun of us but in a nice funny way and I have not regretted telling them or him. Hope I helped :)