what does Gatsby tell nick the night of the accident? why?

Gatsby, in his misery, tells Nick the story of his first meeting with Daisy. He does so even though it patently gives the lie to his earlier account of his past. Gatsby and Daisy first met in Louisville in 1917; Gatsby was instantly smitten with her wealth, her beauty, and her youthful innocence. Realizing that Daisy would spurn him if she knew of his poverty, Gatsby determined to lie to her about his past and his circumstances. Before he left for the war, Daisy promised to wait for him; the two then slept together, as though to seal their pact. Of course, Daisy did not wait; she married Tom, who was her social equal and the choice of her parents.

Through this confession, Gatsby was able to at last convey his true feelings and rationale, or at least what he believed them to be. Gatsby still didn't realize that his dream wasn't real, that the girl he believed Daisy to be wasn't the real, live woman. Regardless, Nick is now able to understand Gatsby's motives and get a glimpse of the real Gatsby. That's why in the end, Nick is able to genuinely say and believe that Gatsby was "worth the whole damn bunch put together."

Source(s): The Great Gatsby

http://www.gradesaver.com/the-great-gatsby/study-guide/section8/