Looking for some advice on co-parenting boundaries. My ex (divorced due to his infidelity) recently introduced his new girlfriend and her kids to our children. I was given absolutely no warning and found out directly from our youngest. I didn't even know he had a partner and he was on dating apps in February so it's very recent.
I am struggling with the lack of respect and communication. It also seems the kids felt they had to keep it a secret from me at first, which I hate. I know his private life is his own, but I feel a simple heads-up was a matter of common decency so I could support the kids properly. I won't go into how inappropriate it is to be already introducing your new partner to young children less than 5 months into a relationship plus introducing the kids to each other as well.
The kids say she is nice which is a good thing, and I am focusing on their emotional well-being by not questioning them and keeping a brave face. However, I am personally going through a rough patch and feeling quite overwhelmed by this. Not only due to the lack of common decency it shows but still being the single one obviously opens up wounds that I would have preferred to have handled without my kids being there.
How do you establish communication boundaries with an ex who ignores basic courtesy without becoming completely absorbed in fury?