So... . How do I maintain disengagement emotionally if I do have to see him?
The truth - accept that you likely will lose your balance a bit, but you have tools now to regain it.
Breathe deeply
Don't indulge in alcohol, drugs, etc before or immediately after seeing him.
Have a cheat sheet (keep it brief and on topic).
Review some of the staying communication tools (they help if situation gets tense).
Remember - you are ok - you really are.