what is the plot development (not summary) of chapter 8?

Nick gives the novel's final appraisal of Gatsby when he asserts that Gatsby is "worth the whole damn bunch of them." Despite the ambivalence he feels toward Gatsby's criminal past and nouveau riche affectations, Nick cannot help but admire him for his essential nobility. Though he disapproved of Gatsby "from beginning to end," Nick is still able to recognize him as a visionary, a man capable of grand passion and great dreams. He represents an ideal that had grown exceedingly rare in the 1920s, which Nick (along with Fitzgerald) regards as an age of cynicism, decadence, and cruelty.

Nick, in his reflections on Gatsby's life, suggests that Gatsby's great mistake was loving Daisy. He chose an inferior object upon which to focus his almost mystical capacity for dreaming. Just as the American Dream itself has degenerated into the crass pursuit of material wealth, Gatsby, too, strived only for wealth once he had fallen in love with Daisy, whose trivial, limited imagination could conceive of nothing greater. It is significant that Gatsby is not murdered for his criminal connections, but rather for his unswerving devotion to Daisy. As Nick writes, Gatsby thus "[pays] a high price for living too long with a single dream."

Up to the moment of his death, Gatsby cannot accept that his dream is over: he continues to insist that Daisy may still come to him, though it is clear to everyone, including the reader, that she is bound indissolubly to Tom. Gatsby's death thus seems almost inevitable, given that a dreamer cannot exist without his dreams; through Daisy's betrayal, he effectively loses his reason for living.