Looking back, I decided to sit with him because he said to the children, "your Mom probably won't want to sit with me". My initial reaction was to say, "what's such a big deal? He doesn't have to incite any emotion in me. I'll sit with him and show all of us that I am civilized and don't care enough about him to need to sit elsewhere".
I'm naturally contrary
But this is where I rely on you level-headed folks. So after some reflection, I am inviting a friend to come and sit with me instead, and I will give up my original ticket. The boys can choose to sit with their father.
I think it will actually be more consistent and less confusing for the children if I leave AH to sit elsewhere.
Thanks for your support and excellent advice!