Jay Gatsby's dream of rekindling his love with Daisy Buchanan ends when he asks Daisy to say that she never loved her husband, Tom, and when Tom reveals the illegal sources of Gatsby's riches. Taken together, these events show Daisy that she belongs to Tom, ending her affair with Gatsby.
Gatsby met Daisy when he was young and in the military; his uniform made him look the same as the richer young men who came by to court her. He realized that he would need money to win her hand, and so after the war, he came back and started building a financial empire that led to enough wealth to purchase an opulent mansion, buy all of the beautiful furniture and clothing he wanted, and host lavish parties. He chose a house across the bay from Daisy's mansion so he could walk out and see the green light on her dock.
After Gatsby and Daisy reconnect, they exchange such a passionate glance at a very tense luncheon at Daisy and Tom's home that Tom brings the affair to a halt. The group drives into New York City, and Tom confronts Gatsby with the information he has gained about Gatsby's sale of illegal alcohol and other financial misdeeds. Daisy realizes that Gatsby cannot provide her the same security as Tom and that she and Tom do have the history that Gatsby wants her to deny, and so the affair dies. Tom is so confident that he sends Daisy and Gatsby back together to East Egg, because he knows that she no longer wants Gatsby.