Assassin in Novel

This is story about Ben Heart who was a normal 35-middle aged man with alot of regrets in his life. If only I hadn't trusted that asshole, if only I hadn't gave up on him, if only I hadn't fallen for that bitch trap. He was just inch away from his losing his insanity. He had started his new life but still he couldn't forget them all for their doings.
He wanted them to die as painful as possible, and he was planning to execute their killing on coming new year vacation. But that was short live as he was teleported to some other world for some reason.