Leon is a law clerk in Yonville. He is one of the good periods of Emma’s life, despite the fact that he was a lover. When first we meet him, Léon is kind of the male equivalent of Emma. He’s young, attractive, idealistic, and romantic to a fault. He wanted to have a lot of romantics in his life. Also, he is extremely bored with small-town life in Yonville and looks forward to the day when he can escape to Paris to pursue his law degree. Leon is initially a young man with dreams of romance and love, but is totally inactive – he’s afraid to tell Emma that he loves her, and instead pines after her until he leaves Yonville.
So, Leon and Emma share a romantic view of the world. When Leon is a law clerk in Yonville, he shares many of Emma’s romantic preconceptions and her love for sentimental novels. He falls in love with her but moves away to Paris to study law, partly because he considers their love impossible as long as she remains married. When Emma goes to Rouen, she was so happy to see him. At this point, Leon is portrayed as awkward and proud, but Emma sees him as cosmopolitan and modern. Drawn to this concept of urban sophistication, Emma begins the affair. At first they are happy, but eventually, they grow bored with one another. When she comes to him desperate for financial assistance, Leon cannot help her and makes excuses while distancing himself from her. After Emma's death, Leon soon marries.
Léon Dupuis in the Essays