AITA Confessions

AITA for ruining my son's sister's first birthday?

My ex's new wife called me three weeks ago and said that she'd just realized her daughter's birthday was on my week. She asked me to please bring my son to the party or drop him off the night before and they'd bring him back the next morning. She was very entitled about it. She presented me with two "options" when I don't have to do either. I said I would think about it and she got huffy and said he has to be at his little sister's party.

I again said I would think about it and she continued to argue, so I hung up. The day before the party I asked my son "do you want to go to (sister's name)'s birthday party?" He said he did so I texted her to tell her we would be there and asked her for the time of the party. She told me it was at noon. So we got there at 12:30 and there were no other cars, which was weird. When we went inside, my ex said he needed to talk to me, and I said that wasn't necessary and asked where the party guests were.

He said he needed to prepare me before I saw his wife. I said "why, is she pregnant or something?" He said she was and I just rolled my eyes. I again asked where the party guests were. He said the party was at 2:00, but they wanted to make sure I had time to put myself together before the party. I told him he needed to quit with the soap opera drama, because I don't have time for it. I took time out of my day to accommodate them, but they blew it. I'm not hanging out with them in an empty house for over an hour, and I'm not wasting gas to leave and come back.

I took my son to the park and we had a nice day, but my ex texted me a bunch about how I was punishing his daughter for the pregnancy. (I don't...