Most Helpful Guy
Ok seriously DONT BE STUPID he's getting pussy where he can before it blows up in his face so just move on cause if he's doing this to her hell do it to you (if he wasn't already since he has a chick so quick after yalls break up)
Most Helpful Girl
You think he is pretending to be someone else with her - yes, he's pretending not to be a cheating asshole and you pretend not to be a sneaky so-and-so who is trying to steal back a a man that doesn't want you any more. You're letting him fuck you for nothing now, it's clear you want him back and it's quite obvious to everyone but you that this will most likely never happen so what are you getting out of this, the sex? The feeling of being second best, a bit of entertainment? You're kidding yourself if you think somehow your love will sort everything out - you broke up for a reason, I'm sure it's still valid.
Gather what little self respect you have left and walk away.