Still thinking about how/when/if I should have a conversation with him about this.
Yep. Give it another 24 hours and then approach. I had this happen and this is how I handled it.
"H, I want to get on the same page about how you handled the change in plans with D7 last week. I felt you put her on the spot, as she agonized about it on our way home. You also didn't ask me if I had plans. So in the future, if you have any inkling that you're going to want to do a switch, will you please talk with me privately first?"
You might want to let D7 know that Facetime isn't a scheduled activity, but that she can always text him if she wants to do it?
Sorry you're stuck in this. It svcks. Been there, done that.
"There are only 2 ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."