I'm kind of questioning the writing of this manga. This isn't just a "I don't want to be like you" scenario, he literally let someone die. And he didn't even bother telling his story, so it doesn't matter if later he says he secretly feels bad about it, because he's a piece of shit for not disclosing his side of the story. He's just a piece of shit and no possible sob story he can tell will correct his behaviour.