Sometimes, they’re genuinely shocked because of self delusion.
When I left my ex, he was well aware that I was tired of the addiction, tired of the anger, tired of the cheating, etc. We’d even tried counselling. Told him, in front of a counselor, that if things don’t change, I will leave.
But he was still “genuinely” shocked when I left. He heard it all, just never believed it.
I’m sorry your ex did that — it was crappy and you deserved better.