Plot summary

In 2002 Elaine "Lainey" Dalton (Alison Brie) causes a scene in a dorm. Taking pity on her as she is about to be kicked out by security, Jake Harper (Jason Sudeikis) claims her as his guest. He learns that Lainey was there in order to lose her virginity to her T.A. Matt (Adam Scott) who Jake thinks is the most boring guy in the world. Lainey eventually realizes that Jake is also a virgin. The two sleep together.In the present Lainey breaks up with her long-term boyfriend Sam (Adam Brody) after telling him she has been cheating on him 16 times. Lainey hates that Sam interrupts her every time she says anything, and never lets her complete a sentence. Sam believes that Lainey cheated on him with his brother, which Lainey denies. Lainey is a kindergarten teacher, but was aiming to go to medical school when she was in college.On the advice of her therapist, she attends a love addicts meeting where she runs into Jake who is there because of his inability to be involved in committed relationships. Jake has just been dumped by his girlfriend Hannah (Margarita Levieva) as he cheated on her with her best friend. Lainey, who has been having an off-and-on-again relationship with Matt the entire time (Matt was the guy with whom Lainey cheated on Sam) learns that Matt is engaged. Matt is engaged to Emma (Katherine Waterston). Lainey still has sex with Matt.On the advice of a friend Kara (Natasha Lyonne) Lainey contacts Jake. Jake & his business partner Xander (Jason Mantzoukas) has just sold their online advertising firm to a company owned by Paula (Amanda Peet). With the sale, Jake becomes Paula's full-time employee. Paula is divorced and has a kid. Jake is interested in Paula, but she is not.Lainey and Jake go on one date (it was a double date with Xander and his wife Naomi (Andrea Savage)) where they confess their sexual problems to one another. At the end of the date Jake confesses that he wants to sleep with her. Lainey decides that the two of them should just be friends and Jake agrees with the code-word "mousetrap" to be used to deflate sexual tension between them.The two hang out more and more and eventually become best friends. Lainey still gets unnerved whenever she runs into Matt anywhere in town. She uses Jake to unload her emotional baggage about Matt and she is unable to move on from him. Lainey also helps Jake understand why women respond the way they do, after he becomes emotionally unavailable after his numerous one-night stands.However, they begin to be mistaken for a couple by strangers and their friends begin to think they are in a relationship as well. Jake finds that Lainey has not had an orgasm for a year, since she stopped having sex with Matt. Jake teaches her to how to reach an orgasm by masturbating the right way.Jake learns that Lainey is going to re-enroll in medical school and possibly move to Michigan. Jake admits that he has feelings for Lainey, and he knows that he doesn't have the right to ask her to stay back and not go to Michigan. He brings her to the birthday party of Xander's child where she meets a man called Chris Smith (Marc Blucas) and begins seeing him to Jake's consternation. Jake, deciding to move forward asks his boss, Paula on a date.A date with Chris Smith leads Lainey to run into Matt and his now pregnant wife. Lainey is shaken to her core and leaves. At the same time Jake has sex with Paula and calls her Lainey. After their nights out Jake and Lainey spend the night together where they realize that they are both in love with one another. They decide to do nothing about it. Jake knows that Lainey has been hurt by Matt.Lainey moves to Michigan and Jake devotes himself to Paula. Two months after Lainey has left, during brunch with Paula, Jake sees Matt and punches him in the face. Paula breaks up with him and Jake is arrested. He calls Lainey from the police station and confesses he is in love with her. She tells him she feels the same way.Sometime later Matt is suing Jake for emotional distress and refuses every settlement he offers. Lainey goes to see him and tells him she will tell his wife about them if he does not accept Jake's settlement. After leaving his office Lainey meets with Jake and the two rush off to be married.