Quote 31
"It was a strange coincidence," I said.
"But it wasn't a coincidence at all."
"Why not?"
"Gatsby bought that house so that Daisy would be just across the bay." (4.147-151)
Gatsby's entire present existence—the house, the money, the pink suits—is constructed so Daisy will notice him. It may look like he's living for the moment, with his flashy parties and careless wealth, but he's actually stuck in the past.
Quote 32
He had passed visibly through two states and was entering upon a third. After his embarrassment and his unreasoning joy he was consumed with wonder at her presence. He had been full of the idea so long, dreamed it right through to the end, waited with his teeth set, so to speak, at an inconceivable pitch of intensity. Now, in the reaction, he was running down like an over-wound clock. (5.111-114)
What happens when you finally get what you've been working toward for years? For most of us, achieving a goal comes with a letdown. Having something in the present is never quite as good as your past self imagined it would be.
Quote 33
As I went over to say good-by I saw that the expression of bewilderment had come back into Gatsby's face, as though a faint doubt had occurred to him as to the quality of his present happiness. Almost five years! There must have been moments even that afternoon when Daisy tumbled short of his dreams – not through her own fault, but because of the colossal vitality of his illusion. It had gone beyond her, beyond everything. He had thrown himself into it with a creative passion, adding to it all the time, decking it out with every bright feather that drifted his way. No amount of fire or freshness can challenge what a man will store up in his ghostly heart. (5.152)
Gatsby's vision of Daisy is way better than the real Daisy. Maybe this is one reason she ends up with Tom—she knows she can't ever live up to who she was for him. (Or maybe it was just the $350K necklace.)