Basil Hallward had gone to Dorian’s home to confront him about the rumors that plague his reputation, and they got into an argument. Eventually, Dorian offered Basil a look at his soul. He showed Basil the now-hideous portrait, and a horrified Hallward begged him to repent. Dorian claimed it was too late for penance and, in a fit of rage, kills Basil.
Explanation:
Basil refused to believe that his supposed friends, Henry and Dorian, were bad. Ultimately, he paid for his optimism and good faith with his life.