The reason he decides to do this is to be on the same social level as Daisy. He starts convicing Daisy to leave Tom for him, telling her that she never truly loved him. Gatsby's plan fails, and as they are leaving the hotel (after a heated argument with Tom) Daisy kills Tom's mistress by accident. Gatsby takes the blame for it. Myrtle enraged husband (George) decides to put an end to Gatsby's life and to his, assassinating Gatsby in his pool.