As for the scouting thing, XW had custody of your son that day. Period. Your choice to go to the scouting event cost him the opportunity to go. Period.
I don't get that. My H has running/track night with the kids each summer. I 100% support him having them those nights although each of them have fallen on "my" night. I do girl scouts with my D9 and my H has always been supportive of that. I don't hold my D9 back b/c my H is going. NC's WAS is an adult and she should be more mature than that.
I think it's hard to understand a WAS like NC's unless you have experienced that. I can say I have and I don't think it's as easy as you describe. Wish it was. I do try to be flexible about most everything, but sometimes things matter (like the fear of your kids being moved away!) and you have to stand your ground. Karen