In chapter seven of The Great Gatsby, why is Gatsby left standing outside his mansion "watching over" nothing?

Chapter seven marks a turning point in the novel because it is at this point that Gatsby sees his dream of getting Daisy finally disappearing from his reach.  In this chapter, Gatsby gets into a fight with Tom in which Tom exposes the truth about Gatsby to Daisy.  Additionally, on the way home from their hotel in NYC Daisy kills Myrtle while driving back to East Egg with Gatsby.  It is at the end of this chapter that Gatsby realizes that the life that he has created for himself in order to impress Daisy is "nothing" without Daisy.  Therefore, he is looking at the "nothing" that will become of the relationship that he was hoping for with Daisy.