well, you should hang out with your best friend a little more, now that your girl doesn't want to be with you...just spend as much time as you can over at his place, and make sure you act all surprised when she keeps showing up!

chances are she's doing this so that you feel guilty (even though you don't know why...women love that). that way she feels less guilty about the awful things she's doing...

and yes, from what you've posted I do think she's banging your buddy. tough luck...but at least she hasn't taken your balls! right? please tell me I'm right...

suggested revenge: turn gay, then get all gay with your best friend so she has nobody left at all! mua ha ha ha (this might not be your cup of tea tho...) You could also start hanging out with HER bestfriend and/or sister and/or mother...that'd definitely up the weirdness factor.