ok i havent had time to read all of the posts cause like you said you need advice before you go ahead and do something stupid... remember this is all my opinion cause i've kinda been in the same situation before...
What you need to realize is, how long has he been your friend? was he the kind of guy who stuck up for you even when you were wrong? was he the kind of guy who had your back no matter what??
in my situation, it was my best friend in the world. the way i see things is "bros before hoes" homie! no girl, and i mean NO GIRL is worth losing your friend over!! If in fact he is a true friend, he'll be there for you no matter what! the only girl who is worth the love of a friend, is the girl your gonna make your wife and your gonna be with FOREVER...
There is a small problem with that though... you don't know who the fuck your gonna be with FOREVER do you?? then since that is a FACT, then you should treat al girls the same til they do something to prove that they are true and that they'll be there for you til the end...
i know it seems like im a womanizing son of a bitch, but that is the truth... cause since i was real young, i treated girls with nothing but respect and treated them like a queen!! you know what i got in the long run? out of the 3 girls i would call my GF... 2 of them cheated on me. WHOREs! and im sorry to say but this 17 year old chick is a whore.
the fact that she was still talking to your homie and about to fuck him most likely.
in my situation i went to my friend first and asked him like a man. i said, "i aint mad but i gotta know the truth... i see you as my best friend but i need to know what happened between ____ and you in the bathroom that night." he told me everything on his side of the story. and i thought aiight koo, imma go ask the girl what her side of the story was. she told me "oh nothing happened we just chilled and talked in there" and i asked for the truth 3 times before i stopped talking to her... i even asked her again 2 weeks after, and she said nothing happened... who am i to believe? the person who took the time to tell me the whole story or the person who said oh nothing happened and then brushed it off like nothing...
hell, i'd rather believe the person who took the time to explain everything that happened that night...
you should do somewhat the same thing... hit up your friend and ask for the truth... if he tells you the truth then ask the chick what happened... if she lies to you then take it like a man. no matter what anyone of them says, remeber that THE TRUTH HURTS!
and just for kicks if she is lying... fuck her one more time, donkey punch the bitch and jam! live your life knowing you still got a friend out of the situation, and got rid of one more whore that wasnt worth your time and effort. Girls will come and go, but those who are real friends will be there for you no matter what.
If your friend starts to get crazy cause your "accusing him" thats when you know he aint your friend. sock him dead in the nose then kick him in the balls and walk away. personally i would rather not fight someone who was my friend. but if you HAVE TO FIGHT, then thats how things are.
PS: if you dont know what a donkey punch is, just ask and i'll let you know lol