My best guy friend and I have been like brother and sister since kindergarten. Freshman year he dated my best friend then she broke with him saying things just weren't working between them. Now as juniors I have developed feelings for this guy but am too scared to say anything in fear of ruining our relationship. My bet girl friend says she can tell I like him and thinks he might like me too and told me the two of them would never go out again because she could never like him more than a friend again. The problem is just the other day when me and this guy were talking headed me to help him ask my best girlfriend to homecoming because he still has feelings for her.
What do I do??

Be calm! I hate how this happens. And I know exactly how you feel. But the only thing you can do at the moment is relax. Keep talking to him like nothing has changed, and also keep talking to your best girl friend. She knows you like him, so she wouldn't do anything to hurt you like that. And if he asks her out, I'm sure you know what her answer will be. You could always just stand up to him and be the one asking HIM to homecoming?

Say you will help him, and do so. When she says she won't go if he asks her, tell him that.
OK - that part was easy.
Now.. I agree with the first responder, you ask him to go with you! Give him a moment to digest the fact that she won't go out with him anymore, (he'll probably want to know every little detail about how she acted), and then say something like 'Well, there's always me if you need someone to go with who you know, and who likes you.' That gives a message that he can interpret either way - old friends, or potential new heartthrobs.