What do you do when you fall too deep for a friend that you know will break your heart?

I've been crazy about this friend of mine, best friend actually, for a very long time. She's quite good at breaking my heart, although she doesn't know the extent of my feelings for her. She’s always interested in other guys, and I'm pretty sure I'm not her type, or at least that ship sailed away long ago. I don’t see my confessing my feelings to her will turn out well in the end. She can illuminate my life when things are good, I can’t be around her and not be utterly mesmerized by her aura, but on the other end of it, she can also make be break down and hit rock bottom. What hurts? As an example: her getting drunk at a party and hooking up with strangers. I'm pretty much bracing my self to just fess up to her and explain why I cannot see her anymore. Why I don’t want to be hurt again. I'll lose one of the best friendships in my life. But also one of the most hurtful ones. I would do anything for her. But if that’s not good enough, it’s probably best if I were to just disappear .