My sisters best friend is 18 I'm 22, she is so amazing and she really knows how to get me wanting her so bad and she can tell I do so bad for years now!, she wears tight clothing and sexy,sexy clothes when she comes around she wants me too she has personally told me (obviously not infront of my sister ) she has told me plenty of times she has always loved me and had a crush on me and we have kissed in secret and it is so amazing!!!.My sister doesn't at all pick up that we are flirting with each other and when I gently smack her bum my sister is completely oblivious to it all.my sister comes home later on a Thursday so her friend comes earlier and then goes to pick her up from work but before that should I do it or not with her friend ? Or is it a bad move to have sex with her best friend? I really, really want her so bad she really has me wanting her like crazy