Even though your relationship with your girlfriend is more of a casual thing, I'd at least talk to your GF about it. Or maybe even tell her mom that she should talk to your GF about it and ask if your GF would be OK with that. You said her mom wants to be your cheating wife. So does that mean she is still married to your GF's dad or stepdad? I'm trying to figure out why she wants to suck you off if she's still married.
