Husband told his BM I’m pregnant first

Why would he tell her that I’m pregnant before we even announced it to anyone? There’s literally no reason she had to know that I’m pregnant so early when we’re not even telling the rest of the world. Or maybe I’m just being overly sensitive because of the fact that he cheated on me with her once in the past. He doesn’t get why I’m upset. And I don’t get why they have to share personal information with each other that doesn’t involve their child. I get that this baby will be their child’s sibling, but now if I have a miscarriage or something she’s going to have to find out.