The love triangle formed by Tom Buchanan's unfaithfulness to Daisy with Myrtle Wilson creates two major problems that are at the heart of the dissolution of Jay Gatsby's ephemeral dream and his tragic end:
1. Knowing that Tom is unfaithful emboldens both Daisy and Tom. After Daisy hears Tom on the phone with his mistress in Chapter Seven, she tells Gatsby she loves him and "Tom Buchanan saw. He was astounded." Daisy's act angers him while at the same time, Gatsby becomes confident enough to tell Tom, "Your wife doesn't love you....She loves me." Gatsby plays his "cards," but loses as Daisy backs down, saying only that she loves Gatsby "now."
2. After a confrontation between Tom and Gatsby in which Tom questions Gatsby's reputation, Daisy begs the group to go somewhere. So, as Nick narrates, they "drove on toward death through the cooling twilight." When Tom, who is driving Gatsby's car, stops for gas at Wilson's station, Myrtle looks out the upstairs window and mistakes Jordan, who sits in the front seat, for Tom's wife. On the return home, Daisy drives Gatsby's car with him; the jealous Myrtle runs out and the drunken Daisy strikes her so hard that she kills her. However, Wilson believes that Gatsby is the murderer of his wife; crazed by this tragedy, he seeks Gatsby at his home later and kills him.