"Your son is going to hurt myself TONIGHT!"
Looks like she was confused here. The mix up in the pronouns "myself" instead of "himself".
She may really have been talking about herself here and got twisted up.
Maybe assure your mom that this really isn't about you, this is your ex possibly talking about herself.
Don't rely on someone respecting boundaries if they've never done it before. It's okay to be done. Sometimes so much happens that the final straw is pretty insignificant alone. It's together all the straws.
Have you read the detaching lessons (over there)? I ask b/c you have a long history of recycling doing something different could help.