Some change was for the better. This wasn't.
It started sometime after Azula was born and Zuko learned how to firebend.
"My brother isn't fit for the throne. I should be the heir."
He became disappointed with Zuko, the son he was once ecstatic about. He started taking an interest in our daughter.
Then he started to plan. I heard him talking about it. I was scared. For me and my family.
The night I left was the night my father-in-law was murdered, cremated to cover the poison up.
I left afterwards to hide myself.
It was for my family.