How do I tell my best friend that I'm bisexual?

As a veteran of coming out, the most important thing I think I can say is to trust yourself. Figure out how you want to tell her. Maybe you want to sit her down at a cafe, or just ask her to listen for a minute. Be honest, make sure to let her know that if she has any questions she can ask, and follow your instincts. It's scary, but most of the time it works out just fine. If you have any questions feel free to message me. Good luck!