Nick walks outside to find his “very young mistress,” Andie, standing on the doorstep. She runs into the house and embraces Nick, and he feels both “relief and horror.” Nick writes that he knows how unlikable having a mistress makes him. Andie chides Nick for not having called her in days, and pleadingly tells him how worried she’s been. Nick ogles Andie’s hair and breasts, and soon she grabs him and kisses him, pushing him onto the sofa and straddling him. As Andie pulls her dress down and places Nick’s hands on her breasts, he can’t help but think of Amy, and he recoils.
The discovery that Nick has been cheating on Amy with a much younger woman makes him look terribly guilty—if not of murder, than at least of being the opposite of the “good guy” he wants to present himself as. From the way he interacts with Andie, it’s obvious that he feels that guilt more acutely than he has at any other point in their affair.
Nick tells Andie that she shouldn’t have come—his sister, Go, is sleeping in the other room. Andie tells Nick that she “need[s]” him. Nick feels himself being overcome by lust—but realizes that to sleep with Andie right now would not only be wrong, but dangerous.
Nick’s behavior in Andie’s presence is gross and lecherous—but he knows that now that Amy is missing, he can’t afford to risk coming off that way.
Nick met Andie when she was one of his students in a class called “How to Launch a Magazine Career.” Though their affair began as just sex, he has come to truly love Andie. Andie doesn’t see Nick the way Amy does—instead of considering him a laid-off magazine writer, Andie only knows him as a successful writer and a teacher with all the answers. Andie seduced Nick, and he let himself be seduced. At home, Amy “slipped past [him] like a fish,” avoiding sex and even basic touch—he found refuge in Andie’s attentions and embraces. One night, in April of the previous year, there was a strange and sudden snowstorm while Nick was working alone at The Bar. Andie came in, and as Nick poured drinks for the two of them, he realized for the first time that he no longer loved his wife.
As Nick reflects on the origin of his relationship with Andie, it becomes clear that he was initially drawn to her because she allowed him to see himself in a new light. After months of Amy’s cold disinterest, a subtle indictment of Nick’s past errors and mistakes, Andie’s interest and kindness made him feel like the hero in his own story again.
After closing The Bar, Nick walked Andie home during the snowstorm, and they had sex for the first time at her apartment. It was the first time Nick had had sex in a long time, and he climaxed quickly. Afterwards, he felt swarmed by guilt—even as he knew there would for sure be a “next” time with Andie. Nick carried on the affair for months and months, promising himself all the while he’d tell Amy and ask for a divorce. Every time he psyched himself up to do so, though, he remembered the money Amy had put into The Bar. He eventually resolved to “drift on,” hoping that at some point Amy would be the one to ask for a divorce—then Nick would “get to be the good guy.” He admits now that this desire “to escape the situation without blame” was “despicable.”
Nick’s inability to come clean about the affair shows that he had—and has—little respect for both Amy and Andie. He can’t choose between the two women, and has kept them both strung along, unwilling to rupture his “good guy” image by admitting to infidelity.
Back in the present, Andie tells Nick that she loves him “no matter what happens.” He is unable to return the sentiment, despite Andie’s pleas for him to reciprocate her unconditional love. He begs Andie to be patient with him and warns her that they will only be able to be together at the end of all this if they’re both very “careful.” He entreats Andie to take Amy’s disappearance “seriously,” and she promises she will—but demands Nick call her once a day, every day, even for just a few seconds, or else she’ll “go crazy.” The two of them begin having sex.
Andie is desperate for Nick’s attention, even as the haze of Amy’s disappearance swirls all around them. Nick succumbs to Andie’s need—he wants to feel wanted and desired just as badly as she does.
Nick wakes up at five in the morning to the sound of Go, in the hall bathroom, running the water. He wakes Andie up hurriedly and hustles her towards the door. He pushes her out, but not in time—when he turns back around, Go is standing in the living room with her hands on her hips. She tells Nick that he is a “fucking idiot.”
Go’s discover of Nick’s affair opens up a new chapter for both of them: Go is finally able to see her twin in a new light, and understand that there are a whole lot of things he’s not telling her.