Talk to her about it. Be straight and say " Excuse me, you know i liked him why are you doing this to me" Try and get to know him better aswel talk alot and be flirty!
be honest with him and tell him how you feel and maby he will tell you how he feels
If this person is truly your best friend, you should be ok with them knowing so go ahead and flirt! XD
They are probably not a very good friend and you should seek friendship elsewhere.
Sha you should! I'd dump this girl she isn't your friend, she's a cut throat.
Enabling
absolutely not. She obviously doesn't respect you at all.
If your friend is really your friend he wouldn't lie about that.
You should still hang out with her, but not as much maybe. She's still your friend though, but if your feelings feel hurt, then just don't go along that much.
Apologizing in-front of the person is the best way. You should go and apologize without others knowing it.
ANSWER: I know it's flattering to have that kind of attention, but if this girl has a boyfriend, be blunt in a nice way and tell her that it's flattering but you don't want her to get in trouble from her boyfriend so she needs to stop being nice to you. See if that works.
You did not "accidentally" sleep with him. You fell and landed on top of him. You flirted with him just to see if you could get him. You did what you did and have to face the consequences. This type of lie never stays hidden. Admit to it, maybe loose a friend, they may break up, or not. Think before you act, it's a lot easier.
Well, if it's a person you admire, you can put Secret Admirer. Or, if it's just a good friend, just put Anonymous, or something similar.