Even still, that doesn't give him the right to be salty AT YOU. He can be salty at the situation. He can be salty that the situation pushed you to disengage. But being salty AT YOU is a bridge too far. In addition to dealing with his crap, you've got your own full plate with your mom, XH and his shenanigans, and your kids. You're even stepping up and in to handle OSS.

This is the ONE THING that you're washing your hands of, and if he can't be grateful for that, then you need to remind him bigly that you're not BM and he needs to seek therapy if he can't tell the difference and react differently to you. I understand needing reassurance (my DH needs it, too), but it shouldn't come with you being the emotional punching bag for feelings he can't learn to work through.

Remember, you've been in an abusive relationship, too. I'm sure you still have triggers, but you picked yourself up and moved forward. Don't let him use his bad relationship with BM for eternity when he behaves poorly, even if it's a rare instance. You aren't her. Don't let him react to you like he would her. Force him to deal with his demons because you've dealt with yours and don't have time to be a crutch that lets him limp along with his just so they can bite you when you can't keep carrying the load. That's not fair.