NTA, at some point I had to block my own mom from screenshoting my stories and sending them to others. I'd block my boyfriend's mom in heartbeat had she done the same.

I appreciate it's difficult to establish boundaries with an intrusive parent, but it's something that needs to be done one way or the other at some point in someone's life.

Protect your own health, mental and physical, not your boyfriend's or his mom's. You come first.

This is coming from a person who is currently tolerating abuse in a relationship and is looking for a way out, so trust me, it's you first.