Tell him how you feel, that you dont like that behavior between the 2 of them and it makes you uncomfortable. I had the same issue with my hb and his ex to the point where she messaged me telling me that they had sex in our bed (this was about a year ago). So after that i told him to stop talking to her, if it doesnt pertain to avery it doesnt matter. And she still tries to talk about other stuff with him but he knows that i dont want to deal with him if hes still dealing with her.
I would have a woman to woman conversation with her. If that was me I wouldn't stand for that for two seconds. There is a difference between beign civil with your ex's and being flirtacious. That's NOT cool.
My hubby and his ex that he has kids with do not act like this at all. The furthest their conversation goes is "I will see you this weekend when I get the kids." Nothing physical and they're always at least 5 feet away from each other. There is no excuse for that behavior and you need to tell that b!tch what's up. I mean girl you're not going to be pregnant forever. You can't just look the other way because you're pregnant!
I feel you 100% my man has a baby momma and @2 kids they are teenagers and she act like they little as girls she talk to him all the time on fb n i try to catch his *** talking to her her said they werent even together and whatnot. Then the ***** jealous of me n my baby and now im pregnant again. Me n my man been together 5 years now so i dont worry as much. I just feel like they have nothing to talk about he said he dont like her. N then. His kids dont ever call him or try to see him they jist want money. I dont know your whole situation but i hope everything is ok