At the end of Chapter Six, Nick describes Gatsby kissing Daisy in Louisville five years before. What is Gatsby giving up when he kisses Daisy?

At the end of Chapter 6, Fitzgerald writes, "He [Gatsby] knew that when he kissed this girl, and forever wed his unutterable visions to her perishable breath, his mind would never romp again like the mind of God."  For Gatsby, kissing Daisy is like marrying her; he is vowing to forever pine for her and live for her from that day on.  Chapter 8 also gives a sense of this vow when Fitzgerald writes, "He [Gatsby] felt married to her..."  This vow would explain why Gatsby pursues Daisy relentlessly throughout the book; however, unfortunately for Gatsby, Daisy does not feel the same way for Gatsby that he feels for her.  For Daisy, "She wanted her life shaped now, immediately--and the decision must be made by some force--of love, of money, of unquestionable practicality--that was close at hand" (Ch. 8).  When Gatsby left for WWI, Daisy was left alone, so when Tom Buchanan showed up, she had that force she was looking for, thus she settled for Tom.