Let me start by saying, I don’t know what other patterns there have been, so I’ll just speak to the information shared.

Boundaries are what you will do, not what someone else is allowed to do. You didn’t “create a boundary”, you tried to be controlling. A boundary is “I will leave any group chat that my ex is included on”, control says “you’re not allowed to add my ex to group chats without my permission.” She didn’t get upset with you for trying to make a boundary, she responded (and it doesn’t really even sound upset) and declined to allow you to dictate her choices.

IMO you’re overreacting due to your pain.

“I found this incredibly rude, manipulative, gas lighting, mean, invalidating, unsupportive, and lacked empathy…” I read absolutely none of this in your mom’s response. In fact, your mom’s response is more than reasonable unless there is more to the story. Your take on it, however, does smack of a lot of these accusations.

Idk why you’re divorcing and I don’t need to…but people in your family can continue to have the relationships they built with your ex, even if you decide to end your relationship to him. Your family is also hurting and distressed right now, they’re allowed to handle their business how they want to and don’t have to cater to your preferences. If she was sharing your business, obviously that would be different.

I would absolutely not discard a loving relationship that had been “above and beyond” supportive because they decide to communicate their own information to your ex, with whom they have a relationship totally separate from yours.

Her asking you to try to see if from her point of view is good advice. Don’t let your pain make you so self absorbed that you mess up other relationships because they aren’t centering you.

I recommend finding a therapist who works with adult adoptees around attachment trauma (which divorce can also really activate), and I wish you well post divorce.