WHY are you sitting with him, for heaven's sake?
He may have the "right" (disgusting though it is) to attend the dance recital. And if the other kids want to sit with him because they don't see him often, that's up to them.
But I see NO reason for you to SIT NEXT TO this deadbeat creep who is making your life so difficult right now. The kids KNOW you are not one big happy family--what is the point of sitting together?
If the tickets are together, then I would ask someone to try to rearrange the seating. Trade seats with another parent or something.
My two cents.