Why does Silas lie to Dove after Bernice's death in the short-story, Witness?

At the end of the story, Dove tells Silas that he is seeing a new woman, a confession that prompts Silas to lie to Dove and tell him that Bernice never loved him. Dove is noticeably heartbroken by Silas's lie, and Silas admits to the reader that he wanted to blame Dove for his sister's death rather than himself.