In Connecticut, Jessica Carpenter and Max Doyle are a high school couple who fall in love after meeting as freshmen, with Max drawn to construction and Jessica aiming to become an orthopedic surgeon. Jessica lives with her mother and a younger sister, and she must contend with the fallout of her parents' acrimonious divorce. She still believes in true love when she allows Max to sneak into her bedroom so they can spend more time together. Their dream is to attend Harvard University.
When Jessica's father, Roger, reveals that his girlfriend, Kelly, is pregnant and they plan to marry, Jessica and her sister are shocked and disgusted. Roger expects his older daughter to tell his ex-wife about the impending marriage. When Jessica sees her mother arrive home after a bad date with a philatelist, she does not reveal to her what her father has told her.
Jessica discovers that Harvard has accepted her. She and Max are ecstatic, even as luck turns briefly uncertain when Max's acceptance is deferred. Matters improve for the couple when Max proposes to Jessica on Valentine's Day; he feels he has never been more sure of anything and that they are ready to spend the rest of their lives together. He loves his fiancée for her optimistic attitude, headstrong nature, and her ability to make things work. Jessica immediately accepts and feels that, in spite of the proposal, she will still attend Harvard.
They announce their engagement plans to both sets of parents. Since Jessica is underage, she requires consent from her parents. Roger feels that his daughter will compromise her university education and does not wish to participate in the marriage, while Max's father supports his son's decision because he believes Jessica is a terrific person and that he and his wife also married young. Jessica's mother Beth makes her daughter promise that she will finish college and use birth control.
On Jessica's wedding day, Roger begs his daughter not to go through with the marriage. Max and Jessica marry and live at Jessica's home, with Beth's blessing. Tensions arise when Max moves his trophies into the room and Jessica becomes slightly uncomfortable with sharing their space. In spite of this, Max and Jessica seem happy to spend the rest of their lives together. Unfortunately, Harvard rejects Max. Jessica demonstrates her resourcefulness when the couple rents off-campus accommodation because they want to be together.
Jessica meets two freshmen, Sophie and Carter. They are curious and surprised about Jessica's marriage. Jessica and Carter share a romantic kiss after he plays his guitar at a local bar, but she tells him that it must never happen again. Tensions arise between Jessica and Max when Max forgets to pay the electricity bill, though he makes an effort to make amends with a candlelit supper. He also reveals that he does not want to attend college, which deepens their strain.
When Max sees Carter and Jessica having a drink together, Jessica stays at Sophie’s for a trial separation from Max. Later, when Max tries to apologize to Jessica, she realizes that he has kissed another young woman. Carter and Jessica spend more time together, culminating in a kiss that she ultimately stops. Outside Carter's place, they run into Max and another young woman, and both Max and Jessica temporarily move back to their respective homes. Max's parents encourage him to consider annulment or divorce, while Jessica's mother advises her that a true test of a strong marriage is the ability to weather challenging times.
When the couple has dinner together, Max reveals that he has started to fill in college applications and that he has been offered an internship at an architect's office. The film ends with Max and Jessica making a concerted effort to rebuild their marriage and navigate a future that remains hopeful, even as it stays uncertain.
