With his hands around Amy’s throat, Nick wonders who he would be if he killed her—who he would be without her. He lets go of Amy and she rasps and coughs as she catches her breath. He doesn’t want to be a killer, just like she tried to make him seem to be, and the sickening knowledge that he truly would be no one without Amy hits him hard. Nick concedes that Amy has “brought [him] to heel.” He is dependent on her, as much as he hates to admit it.
Nick doesn’t want to give into Amy’s narrative of him as a killer—the only alternate is accepting the narrative that he can’t live without her. Amy has presented Nick with two evils, and he chooses the lesser—but remains aware that she’s the one writing the story now, and he’s powerless.
At the same time, Nick knows that just as Amy made him into his best self, he made her into her worst self. He demanded she turn herself into someone else for him—and drove her mad in the process. He knows that now, it is up to him alone to stop her—not kill her, but simply stop her.
Nick still isn’t willing to accept total defeat, and remains determined to challenge—if not bring to light—the narrative Amy has foisted upon both of them.