In similar situations I prepare myself with some positive internal chatter. Phrases, thoughts, sometimes even just slogans help me stay centered. My internal chatter can be quite detrimental if I don't pay attention - and for me that leads to increased self doubt and confusion. I also have some canned responses that I can just spit out. I used to actually practice them.
I plan escapes. If I feel weird, iffy, unsure, confused, angry, or any tiny bit out of control - I just get away
Perhaps not the best coping mechanism but since I don't actually want him in my life, need him in my life, etc. getting away from him seems to be a pretty solid coping mechanism so far so I go with it. I justify it by making sure I do not play any games. I do not lead him on in anyway, say or do anything that would give him the idea that I am willing to engage in anything besides co-parenting. I never used to give myself permission to leave or even ignore. At an emotional level I was not really a separate person. I am now and I leave.
Hope some of this helpful. You have the strength and recovery to manage this next step - just stay focused on that and not him!