It is in Chapter 7 that Gatsby and his guests decide to go to town. Remember at this stage that Daisy, Tom's wife, is having an affair with Gatsby and being very indiscreet about it. It is clear that Tom suspects that something is going on. Gatsby at first suggests that they all go in his car, but then Tom says Gatsby can take his car and Tom will drive Gatsby's car. He tries to encourage Daisy to go in the car with him, however, Daisy tells him to take Nick and Jordan with him and she says that she will go with Gatsby.
The language that is used that describes how she moves to Gatsby away from her husband is very important to note. For example, when Tom tries to get her to go with him, she "moved out from the circle of his arm." Then, having told him to take Nick and Jordan, she "walked close to Gatsby, touching his coat with her hand."
It is clear that Daisy is being very obvious about he affair with Gatsby and almost flaunting it in front of her husband. Of course, we know that Tom is likewise having an affair with Myrtle, so the hypocrisy and deceit is something that both people are now experiencing.
When Daisy, Tom, Jordan, and Gatsby have luncheon, Daisy and the others "drank down nervous gayety with cold ale." But suddenly she asks, "What'll we do with ourselves this afternoon...and the next thirty years?" In another act of spontaneity, they decide to drive to town.
Since she has renewed her erotic relationship with Jay Gatsby after her fling with him years ago before she was married, Daisy has not been very discreet about her feelings for him. In fact,
She had told him [Gatsby] that she loved him, and Tom Buchanan saw.
Shortly afterwards, Tom interrupts Daisy as she talks with Gatsby, and he tells the others that he is willing to go into the city. When Daisy tries to talk with Tom, he ignores her. So, she says, "Come on Jordan." As Tom comes out of the house, Gatsby suggests that everyone go in his car. Tom asks if Gatsby's car is standard shift, and Gatsby answers that it is.
"Well, you take my coupe and let me drive your car to town."
Although Gatsby finds this suggestion repulsive; he avoids answering directly by saying that there is little gas in the car. But Tom "boisterously" interjects that he can get plenty of gas at a drug store. "You can buy anything at a drug store nowadays," he adds with hidden meaning. Turning, he invites his wife to ride with him, calling to her, "I'll take you in this circus wagon." But she moves away from Tom and rides with Gatsby in her husband's car. Tom and Nick and Jordan all climb into the front seat of Gatsby's car. "'Did you see that?'" Tom demanded." after they pulled away Then, looking at Nick, Tom realizes that he and Jordan have known for a while about his wife's unfaithfulness.