Quote Originally Posted by Ae...
Well it's kind of obvious you need to stay away from this girl that's ratting you out. If you say that can't work because you're all in the same group of friends then maybe you should not say or do anything that could "incriminate" you...or maybe you should take off and find some new friends.

Actually man tell that girl to fuck off, if your other friends take her side then they weren't very good friends to begin with given the circumstances.

Can't really grasp your situation though, it seems really pointless this girl is telling your sister everything you're up to for no apparent reason. Fortunately for you, there are good people on this site who will more than likely give you better advice than I can.
I think that's about the best advice I could give anyways...