“Cartas de amor traicionado” is one of the short stories in the collection “Cuentos de Eva Luna” by Isabel Allende. The English translation of the story is entitled “Letters of a Love Betrayed.”
In the story, the orphan Anilía has spent seven years at a convent in the foothills of the Andes. Anilía's uncle wants to take her only possession, a piece of land. The uncle's son Luis sends love letters to Anilía that persuade her to marry him. Luis turns out to be a violent man, and Anilía goes mad. After Luis dies, though, Anilía discovers that the letters were written by her son's schoolteacher, with whom she falls in love.