Why does James Vane not kill Dorian when he has the chance to do so?

James Vane hesitates to kill Dorian Gray when he has the chance because he realizes that Dorian is not the same man who harmed his sister, Sibyl Vane. Dorian's charm and youthful appearance disarm James, causing him to question his intentions and the morality of his revenge. Additionally, Dorian's insistence that he has changed and his plea for mercy create doubt in James's mind, ultimately leading to his decision to spare Dorian's life. This moment highlights the themes of redemption and the complexity of human nature in Oscar Wilde's narrative.