Nick thinks that Gatsby's dream cannot be achieved. The death of Myrtle will anger Tom much more than before, so he wouldn't let Daisy go to Gatsby. Although Daisy killed Myrtle, Gatsby said he want to put all the fault on him. Thus, Tom would think Gatsby as an enemy and never do whatever Gatsby will like. Gatsby has no choice but getting all blame to protect Daisy from Tom.
This quote shows that Gatsby is desperate to have Daisy. He thinks all the pasts can be repeated again. Nick tells Gastby to give up since Daisy is married and can’t be divorced. But, Gatsby see nothing but getting Daisy. Since Gatsby loves Daisy so much that noting is the matter for him. We can say that he almost spent half of his life for Daisy. It was not direct but indirectly. He built his huge mansion to show to Daisy. All of his parties were for Daisy to come and enjoy. Gatsby stayed close to Nick because he was the second cousin of her.