Your Mexican girlfriend has always been pretty liberal since college. You mentioned a MFM to her which would involve one of your coworkers, someone she has never met. You assured her "he is a nice guy". You were surprised she didn't ask any questions and said, "Bring him over".
Well you did. She mounted him in a way that would give her deepest penetration. Your friend even had the chance to suck on her cute little pointy titties. She blows you off because she knows you're going to fuck her next.