I'm the Villain—Can’t I Resign?

I possessed the body of a villain whose inferiority complex leads him to commit one foolish act after another—until the protagonist tears him limb from limb. Since it all happens because he kills the protagonist’s younger sibling, I devoted myself to keeping that sibling alive, then handled the cleanup so I could resign safely. So how did things end up like this? Now the protagonist has completely lost it, insisting he can’t let go of the person who became his lifelong benefactor.