Went out to a bar with my girlfriend and her team for the after party. They are a really close group both physically and emotionally. I meet the ex and shit was cool.

Right before last call we were all outside smoking a cigarette. The ex was rubbing my girlfriends back, something I noticed but didn't care all that much about. Until the ex shoots me a grin. I hold eye contact and grin back, before girlfriend changes position and the ex stops. At the end of the night my girlfriend comes home with me so I'm not uncomfortable with the actual act of back rubbing, just the dick grin that accompanied it.

I'm not sure if I handled this well or not. I didn't know what to say and I didn't want to come off as insecure. This was my first time meeting the majority of the team. The few that I've met before, have stated that they think I'm better for K than her ex and that they really like me.

What could I have said or done that would have been better in this situation?

I'm probably going to see her ex (and others) pretty frequently in the future so it's important to me to not make things uncomfortable but I'd like to be in control.