Jon Martello is a young man from New Jersey who prides himself on his physical appearance, apartment, family, car, and church habits. Known to his friends as "Don Jon" for his ability to land a different woman most weekends, he also harbors a secret addiction to pornography, which he finds more satisfying than real-life relationships. Jon lives in a cyclical routine: clubbing, one-night stands, and weekly confessions at church to absolve his sins. His life takes a turn when he meets Barbara Sugarman, a beautiful and assertive woman with very traditional views on relationships and sex. She sets high expectations for him and pushes Jon to improve himself in various ways, including attending night classes.

As Jon's relationship with Barbara develops, he struggles to reconcile his virtual fantasies with the realities of an actual relationship. Barbara's desire for a romantic and idealized relationship clashes with Jon's reliance on pornography. Simultaneously, Jon enrolls in a night class where he meets Esther, an older woman dealing with her own personal losses. As he navigates these new connections and the conflicting needs and expectations of those around him, Jon begins to question what truly brings fulfillment and satisfaction in his life. The journey compels him to re-evaluate his understanding of intimacy, connection, and the meaning of true happiness.