How does Gatsby die?

All of the characters contribute to Gatsby's death, escpecially Daisy because he loved her and she didn't want to leave Tom for him. The fact that Tom is having an affair with Myrtle contributes to Gatsby's death because if it weren't for the affair, Gatsby would have never been involved with Myrtle's death. Everyone's greedy grabs for the "American Dream" was the cause of Gatsby's death.

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More precisely, when Gatsby and Daisy were driving together in Tom's car, Myrtle came out and waved at them. Daisy decided not to swerve the car away and ended up killing Myrtle (most likely because Myrtle was Tom's mistress). Tom told Wilson, Myrtle's husband, that Gatsby was driving the car, so Wilson decided to go and take revenge by killing Gatsby.

Thus, Tom's affair with Myrtle triggered Daisy's hatred for Myrtle which triggered Myrtle's death which triggered Gatsby's own death by the hand of Wilson.