DRAFT
In spite of being separated for over 2.5 years, being divorced all summer, and the on-spot observation that both my ex-wife and I are better human beings when not in each other’s presence, my daughter wanted to have dinner with both of us. She is 11. I get it. When she took a long time on her birthday wish before blowing out the candles, I could only guess at what she was thinking. She has not held back for a moment on letting us know at every moment what she is thinking and feeling (including reconstructing the former version of the family). She does not wear her heart on her sleeve, but displays it on a large dirigible that is constantly circling overhead.
When she is angry, it’s not much fun, but at other times, when she is feeling generous, compassionate, kind and loving–which is quite often, actually–she is a contagious source of happiness.
So, in a way, even though she can be volatile, doesn’t worry me. I know what she is thinking. I know what she is feeling. And because I know these things, I can (usually) work with what I have with some sort of solid footing. She wants her mom and me–and her brother–together with her on her birthday. I can do that. I can behave, be sociable, and suppress the gunpowder when the ex either intentionally or unintentionally goes to light the fuse, which is easily ignited around here.
My son, on the other hand, is a cipher. In these past 2.5 years of separation and wrangling, he has only said one sentence about the divorce, in an aside to his sister. I have no idea what he is thinking. I do not whether he is angry, sad, OK with it, or–using his most commonly used adjective these days–annoyed.
I made it through the dinner. The ex-little woman made it through dinner (didn’t bat 1.000, but was close). I’m not in the unbiased position to judge my own behavior.

That drawing is absolutely correct about the feeling engendered by divorce although I am not sure it should be that way
I think you are amazing to have this family birthday dinner together with your ex, for your children in spite of all you have been through.
Thank you
You did it. You do it for the kids, as authentically as you can, for a grown up. They will remember that it was hard, for each one of you, for different reasons, and YOU cared enough about them to be there…
You assume too much of the burden,. Spoken as your father