Do you think you would have reacted that way if he was taking her on vacation over your weekend? I suspect you would. I would have too before my give a fuck was broken.
I would have been hurt/angry that he was ditching his kids for OW. I would have been hurt/angry that he was spending Thanksgiving with OW. I would have been hurt/angry at the way he was treating me. So many things to feel hurt/angry about. I get it. It hurts until you detach sufficiently.
He yanked your chain and you reacted - we all do until we decide not to anymore. I don't know that the urge goes away of its own volition - its something you have to work at and it takes practice.
Next time.....a simple answer and then crickets.
^^Absolutely. Remembering what it feels like right now will help you stick to this.
NC = No New Hurts.
You've so got this.