As Borboletas Também Amam (1979)

Monica, a naive schoolgirl from a suburb of Rio de Janeiro, meets Virginia, a former neighbor, now living in Copacabana. Influenced by her, she decides to take on a double life: in the morning she is the suburban girl, in the afternoon she attends a brothel in the South Zone. One day she meets Flávio, a friend and eventual lover of Virginia. Flávio falls in love with the purity of Monica and wants to drive away her friends, for considering Virginia a bad company for her beloved. Going back to class, Monica discovers that the math teacher, Raimundo, is one of her most frequent clients. Flávio, upon learning of her double life, invades the brothel and meets his father, Raimundo. Threatened, father confesses: Flávio is not his son. His mother, Matilde had given herself to a stranger to have a child, since he is barren. Seeing his secret revealed, the mother commits suicide.