Léon Dupuis is Emma's second lover: in Part II, a young clerk of the notary Guillaumin in Yonville, who loves her without declaring himself; in Part III, back from his studies in Paris, the lover with whom she meets every week in Rouen.
At the Bovarys' dinner on their arrival, Léon and Emma discover the same tastes: the sea, which according to her "conveys ideas of infinity," reading, novels. In the evenings at Homais's house a complicity grows in which nothing happens. Léon writes letters that he tears up, finds Emma "so virtuous and unapproachable" that he gives up all hope and leaves for Paris; the parting ends in a handshake "in the English manner."
He reappears at the end of Part II, at an opera in Rouen, and shortly afterward, leaving a meeting at the cathedral, takes Emma into the cab with its blinds drawn. Three days follow that the text calls "a true honeymoon," and then the Thursdays at the hotel. Gradually the roles reverse, and "it was he who really behaved as if he were a mistress." Pressured by an anonymous letter sent to his mother and by his employer's warning, he begins to see Emma as a risk to his career; when she, ruined, asks for help, he comes back empty-handed and escapes with the lying promise of money from a rich friend. After her death he marries, and Charles sends him congratulations.
Léon gives Emma back the romantic vocabulary she herself offers him; Rodolphe uses it out of calculation. The novel shows him as a weaker version of Emma's mechanism: sentimental ambition without the courage to sustain it.