TLDR caught my brother with another chick while his gf is none the wiser. They're both 20 year olds but I'd be lying if I said I wouldn't fuck his gf if given the chance and part of me wants to let her know and then she if she's down to revenge fuck and cuck him. I'm not too close to the guy and he pulled an awful fucking stunt the other day which left a bad taste in my mouth. Also if she is down what would be a tell to know she is? Any advice is greatly appreciated.