"Bart's Friend Falls in Love" is the twenty-third episode of Season 3.
Milhouse's relationship with a new girl at Springfield Elementary, Samantha Stankey, causes them to spend all of their free time together. This causes Milhouse to stop spending time with Bart, much to his friend's irritation and their friendship becomes more distant in the process. Meanwhile, Homer tries to lose weight by listening to a subliminal tape.
After a close encounter (Indiana Jones style), Bart manages to retrieve Homer's jar of change to take to school. Bart makes his way outside the house where Otto was waiting and boards the school bus leaving Homer shouting angrily at Bart as the school bus drives away. His best friend, Milhouse, is holding his Magic eight ball. Bart asks the ball whether he and Milhouse will still be friends by the end of the day, and the ball predicts 'no'. Both are puzzled by how this could happen.
A new girl from Phoenix called Samantha Stankey starts at Springfield Elementary School, and Milhouse falls in love with her. To Bart's dismay and anger, Samantha reciprocates, and the couple spend all of their free time kissing in Bart's treehouse. They ignore Bart, and he takes off, he soon tries hanging out with Martin but it doesn't work. When the couple goes to an alien movie, Bart joins them. Afterwards Bart suggests more fun ideas for them to do but Milhouse asks Bart to not spend time with him and Sammantha so much. Bart walks away angry but after going into an alley he starts crying. Seconds later, Milhouse asks Bart if they can still use his treehouse, Bart tells him no but changes his mind when Milhouse mentions that if Sammantha's dad catches her, he'll be furious.
Meanwhile, Lisa is watching a documentary on the health problems of obesity. She is fearful that Homer's obesity will lead to an early death. On Lisa's suggestion, Marge orders a subliminal weight-loss tape for Homer. Humorously enough, the company is out of the tapes and sends Homer a "Vocabulary Builder" tape instead. Homer ends up eating more than ever, but his vocabulary is through the roof. When he realizes that the tape is hopeless he gets rid of it, and his vocabulary quickly returns to normal.
In order to restore the previous status quo, Bart tells Samantha's father what's happening. Mr. Stankey rushes to Bart's treehouse and after seeing what happened takes her away before she can even explain. She is sent to Saint Sebastian's School for Wicked Girls, an all-girls convent school, never to see Milhouse again. After she leaves Bart thinks that everything will go back to normal right away says they should go to the arcade but Milhouse is in no mood for that as he is heartbroken. Overtime Milhouse remains depressed and Bart starts to feel guilty for his actions. After failing to get help from Homer (frustrated over the vocabulary tape), he turns to Lisa for help who is reading a magazine called Eternity and tells him he will have to bite the bullet and confess. He visits Milhouse and confesses that he snitched on him and Samantha to Mr. Stankey. Humiliated, he and Bart fight over Bart's actions much to the delight of Milhouse's parents. Then Bart ends the fight by hitting Milhouse with the magic eight ball, destroying it in the process and calming themselves down. Milhouse visits Samantha at the convent school and Bart offers an apology to her, but she says that it is okay - she loves Saint Sebastian's. However, she still has feelings for Milhouse and gives him a farewell kiss, despite her knowingly violating school rules.