Why does a girl rub your back when hugging?

oh honey that means the hug is over. Sure you may never want to let go but obviously he is done. If he is rubbing you on the back during a hug now that's different that's more of a sensual action if he is just patting you that means " okwe've hugged now I'm done." so here's what you do, pat him back and pull away before he gets a chance to end the hug first this way you're playing hard to get and he will feel like the hug has been cut shorter thanhe wants thus since he will feel like he can't have you he will automatically like you more and want to hang on longer thus ending the patting on the back. Make since? See it's just human nature for people to want what they can't have. It will get them every time.