Baby Mama Drama

The guy I’m dealing with has a baby. Him and the mother of his child are still friends. I have no problem with her texting him & whatever about the baby but when it goes left & she’s trying to do other things but co-parent that’s when I have a problem. Recently it was her birthday & she drove all the way down to where he lives (4 hour ride from her house) to go to dinner with him. Now he told me & I tried to act like it didn’t bother me until I seen how nice the restaurant was & it looked like a place we as a couple would go. He made a comment “you bitches come after her” turned me off & we haven’t had a normal conversation since that day. I’m not quite sure how to handle this, I’m 20 and never took a man with a child serious because of my fear of things like this happening.