Why does gene say that he wanders through the night he does not exist?

Gene's nighttime wanderings lead him to a tragic realization. As he floats aimlessly, he comes to recognize that he has no sense of himself, no sense of his own identity or being. Gene has spent so much of the novel losing himself in Finny that, once severed from him, he feels himself to be a ghost, departed from the world of the living. This spectral existence renders him deaf to the profound lessons that his world has to teach him; it cuts him off from a meaningful life