Its difficult, I am sorry you are dealing with this. I understand the "adult in the room" comment all too well. My ex wife is emotionally, no older than 8 years old. Over the past year, I only respond to messages about our kids that absolutely require a response. Nothing else. Ever. Its what I found the cleanest way to break free and live my life to the fullest. She is sick beyond any help. The constant lying, attempts to get my attention, its so sad.
Be patient with yourself, there is no playbook for this. If you can find a way to presence, that is, only living in the now, your suffering will ease and a new world will emerge. Be well.