Although he looks like the stereotypical All-American Guy, Nick is actually a deeply insecure and morally weak man who blames his wife for all of his troubles. He is originally from Missouri, where he returns with Amy after losing his job as a writer in New York. His abusive father Bill’s insidious misogyny has invaded every aspect of his relationship with women, and seeing Bill fills Nick with shame for his own attitude toward his wife. Nick co-owns a bar with his twin sister Go, which he bought using Amy’s money and to which he often retreats to hide from her. He and Go have an extremely close and enmeshed relationship, to the point that people have made incest jokes to them their entire lives, and they are constantly navigating an awkward and unspoken set of boundaries. This closeness also makes Go’s relationship with Amy challenging, as she and Amy can't stand each other, and each resents the other woman for her closeness to Nick. Nick knows this, and alternates between playing into this division and trying to fix it. Nick appears laid-back and affable, but hides his worries and insecurities behind both humor and anger. He struggles with the traditional masculine roles that society and Amy’s parents expect of him, feeling emasculated by Amy’s inherited wealth and by his own inability to provide for them.
When Nick’s relationship with Amy really begins to deteriorate—after he forces them to move to Carthage and leave their life in New York—he begins an affair with Andie, a student in her early 20s from his writing class. Nick feels guilty about sleeping with Andie, but she's young, attractive, and worships him, which Amy has ceased to do. When Amy disappears, Nick’s shiny surface is part of the reason the public turns against him so quickly. His easy smile and apparent inability to look upset or worried on camera make America suspicious that he doesn’t care Amy is gone. He’s desperate to be liked and to look like the good person he believes himself to be, so he struggles with the media’s portrayal of him as a cold-blooded wife-killer. When it turns out to be Amy who’s the murderer, Nick still can’t summon the backbone to leave her. Despite learning the full extent of Amy's deceit and manipulation, Nick decides to stay with her when he finds out that she’s pregnant with his child. This is only part of the reason, however, as others around him observe. Nick’s whole character is built around being Amy’s husband. He thought he was the protagonist of his life, but it was his wife the entire time.