<human>: Hey guys, I'm hoping to give some back story and then jump into the problem.

Last summer when we were not talking, my girlfriend got drunk at a party and almost had sex with her best-friends brother. The only reason they did not is because he had whisky dick. She says hes only viewed as a brother to her now.

I guess that situation makes me feel unconformable and is recently brought to light because my girlfriend, her best-friend and her brother have been hanging out again. I then see on someone else snap-chat that he has his shirt off and my girlfriend is rubbing his back.

Should I be concerned about this behavior? Should I confront her?

Could you distill the essence of the text into 1-3 sentences?
<bot>: Girlfriend hanging out with guy she almost hooked up with, now see her rubbing his back on social media. She knows things like that make me uncomfortable and she also does not do those things for me if I ask.