What is the overall theme in Chapter 7 of "The Great Gatsby"?

In chapter 7, the dream that Gatsby has been chasing during the entire novel begins to dissolve in front of his eyes. He has spent the entire book chasing after Daisy and even dismissed all of his servants so that no one will spread gossip about his afternoon visits with her. However, Daisy proves to be fickle and "unworthy" of Gatsby's dream when the group heads for New York. Tom begins to accuse Gatsby of being a bootlegger and of other assorted crimes and Daisy's affection begins to wane and she retreats“further and further into herself.”

But Gatsby naively hopes that she will leave Tom for him. After Myrtle's death, Fitzgerald points to the hopelessness of Gatsby's dream in the last scene. Gatsby is afraid Tom will find out that Daisy was the one who was driving and killed Myrtle, so he is standing watch outside of Daisy's house. This image reminds the reader of the first image we saw of Gatsby looking at the green light on the dock of Daisy's house. Only this time, Nick describes Gatsby as “standing there in the moonlight—watching over nothing.” Nick has realized Gatsby now has nothing and his dream is destroyed. The destruction of Gatsby's dream also symbolizes the destruction of the American Dream, that if we work hard enough, we can achieve anything. Gatsby worked hard and in the end, never achieved what he really wanted.