Plot summary
Thirty-year old sound engineer Connor is infatuated with prickly, sardonic Olivia, who is afraid of feelings and commitment. Their mutual friend, Greg, encourages Connor to approach a young woman who had been stood up for a date, who turns out to be Jenny, a graduate student still living with her parents. After Olivia jealously inserts herself into their flirtation, the three go drinking and dancing together, culminating in a threesome.
In the morning, Olivia panics over her emotional interest in Connor and leaves early. Despite his feelings for Olivia, Connor has shower sex with Jenny. He then tracks down Olivia and convinces her to give him a chance at a relationship. Their first date goes well and they become inseparable, sharing a blissful 6 weeks in a whirlwind as a couple. Olivia soon discovers she is pregnant. Despite her initial uncertainty, Connor's elation at the news leads the couple to assert their mutual love and begin happily planning their future together.
Jenny appears on their porch and reveals that she is also pregnant by Connor. Olivia is devastated to learn that the baby is the result of Connor's solo tryst with Jenny a mere half-hour before he begged Olivia for a chance. Deciding that she cannot have a future with Connor as long as Jenny is involved, Olivia ends their relationship and resolves to get an abortion.
Despite mourning the loss of the idealized future he envisioned with Olivia, Connor insists on supporting Olivia and driving her to the out-of-state appointment. His kind and compassionate behavior throughout the trip reignites Olivia's feelings for him, and she backs out of the procedure. On the drive back, Connor sees a text message from a former partner of Olivia's whom she'd had a one-night stand with in the wake of her and Connor's breakup. Hurt that Olivia slept with someone else instead of trying to work things out with him, Connor breaks up with her.
Connor begins supporting Jenny more, causing conflict when he obliviously does insensitive things like take Jenny to Olivia's doctor instead of finding a new one. When Connor learns that Jenny has been lying to her parents that she and Connor are together, he goes along with the charade. Though tempted by the promise of a simple, uncomplicated life with a devoted, conventional wife like Jenny, Connor cannot get past his infatuation with Olivia.
During a fight, Olivia points out that the situation gives Connor bragging rights for getting two women pregnant, while making her look stupid and gullible for having his kid. Despite her previous standards, Olivia confesses that she still loves Connor and has been fantasizing about getting back together. Connor is thrilled at the prospect.
Olivia's married fling shows up. Shocked at her pregnancy, he confesses that he never had a vasectomy, as he previously claimed, and could potentially be the father. Olivia secretly gets a paternity test, but goes into labor before receiving the results.
Jenny and Olivia end up giving birth on the same day. Tension escalates when Jenny's parents discover the truth about her situation, and Olivia discovers that Connor is not her child's father. Upon learning this, he leaves to attend the birth of his real child. Jenny gives birth to a daughter.
Several months later, Connor and Jenny have been successfully co-parenting, and Jenny is moving into her own house. Olivia shows up on moving day with her own daughter, whom she has named after Connor's great-grandmother, and confesses her love for him. Connor agrees to give their relationship another try.
In a post credits scene, Connor's best man Greg decides to tell the story of Connor, Olivia, and Jenny during his toast at Connor and Olivia's wedding.
