I don't know at what point it stops but I generally try to take things one day at a time. If this is what my kid needs today, then good and tomorrow is another day.
Honestly, I have yet to meet adult child of divorce who've told me they were glad their stepmother/father kept coming to events inspite of the tension and quite a few who've shared stories of wishing none of their parents had come to games/graduation/their wedding because of the unspoken, ever present tension.
I don't have an exhusband, and I've not seen it in this thread, but far too often I've seen children's activies and big days used as the modern day way of, excuse my language, pissing to mark ones territory. In one year I had two good friends who had to deal with the "crisis" of divorced parents current spouses being upset with my friend that she wanted a picture of just her and her parents.
As I said, I don't have an ex but it is strange for me to read, especially here of all places where children are so respected, that the default is to put the adults feelings ahead of the kids.
ETA: I also think that for someone who has spend his entire life with everything in his life split in half he benefits greatly seeing the people in his life have some unity celebrating him even if it is hard and uncomfortable for the grown ups.