Keep in mind the title

It's not "reform a villain "

The Tale of the villain.
Has NO redemption arc.
It's the mc that eventually gives way to how things are.
They stay together.
Ml treats him slightly better after mc completely gives up on life but no redemption.
There's no character reform when the character is a sociopath.
It's usually the victim accepting they want to be with them because of the small kindnesses sprinkled in between all the abuse.