Why does nick suggest that gatsby go away even though he knows that it was daisy who killed myrtle?

Nick understands that Daisy will never be ready to leave Tom and go with Gatsby; she has her own demons from her past that Tom is well aware of and is able to help her overcome. Nick also knows that Daisy will never admit to what she has done, so Gatsby will pay the ultimate price for the murder in one way or another.