Quentin can’t really feel empathy, at least not in the traditional sense. He certainly feels a need to preserve the well-being of those close to him, which can outwardly present itself as empathy sometimes, but that’s about as close as it gets. Although the nature in which he cares for people is mostly self-centered and self-serving, he will still be extremely protective over people he cares about and anyone hurting them will make him very angry. This has only ever applied to a few people in his life, Rosie for the most part, and also Emmett and Dolly somewhat. Also, the more he cares about someone, the less he’s willing to hurt them himself or will fantasize about it. With Emmett and Dolly, he certainly had times where he wanted to hurt them and would have enjoyed it. He did not feel that way about Rosie, which is why him accidentally killing her was so devastating for him.