Made the catastrophic mistake of sleeping with best friend's on-off boyfriend last week. She has now dumped him on account of knowing he slept with someone last week, she then told a friend of ours that she knows who he slept with and that it is someone she (the friend) knows. She is acting totally normally with me but I'm starting to think she knows it was me and is just trying to see how long it takes before I cave in and tell her.
Thanks for all the advice (constructive and destructive), the situation's now resolved, it's all out in the open and she is fine with it - incidentally, he was an "off boyfriend" at the time. I've since decided to remove myself totally from the situation though especially now that the two of them are back together and she's just found out she's pregnant with his baby. Yes I am a bast*rd and probably deserve everything I get - believe me, I know that more than anyone.