In this paragraph from Chapter Eight, Nick is informing the reader of the early history between Gatsby and Daisy in which they first met in Louisville and almost married. By doing this, Nick makes an important allusion to the Holy Grail, the cup which was purportedly used by Jesus Christ at the Last Supper:
But now he found that he had committed himself to the following of a grail.
In terms of Gatsby's dreams, this allusion suggests that Gatsby dedicated his life to pursuing Daisy in the same way that people have sought to find this elusive cup. It also implies that, like those who seek the grail, Gatsby loves Daisy so much that he can never truly let her go. Moreover, Gatsby knows that if he keeps trying, he is sure to win Daisy back someday—he is just not sure how long it will take.
But he didn’t despise himself and it didn’t turn out as he had imagined. He had intended to take what he could and go, but now he found that he had committed himself to the following of a grail. He knew that Daisy was extraordinary but he didn’t realize just how extraordinary a “nice” girl could be. She vanished...leaving Gatsby—nothing. He felt married to her, that was all.
In Chapter 8 of The Great Gatsby, Gatsby reveals more of himself to Nick, while at the same time he begins to realize the emptiness of his dreams. The passion that he once possessed when he "took" Daisy has transmuted into the same concept as his dream of wealth: simply the gaining of his dream, that which he has desired. Daisy becomes a part of Gatsby's American dream, the charm of money--that voice that "sounds like money" has, however, become "a deathless song." For, Daisy has become symbolic of all that Gatsby desires as his is the drive in the "service of a vast, vulgar, and meretricious beauty." Indeed, Daisy is the objective correlative of this "meretricious beauty" of wealth as the American Dream. Gatsby's dream is illusory and vulgar; later, he learns "how grotesque a rose can be," having apprehended the lure of materialism as a vulgar pursuit that is unsatisfying and deceptive.