I have committed the worst sin that can be committed. I have not been happy.
He cometido el peor pecado que uno puede cometer. No he sido feliz.
Original text (English)
Notes from Wikiquote
"El Remordimiento" [Remorse] in La moneda de hierro [The Iron Coin], as quoted in Borges at Eighty : Conversations (1982) edited by Willis Barnstone, also in Hispanic Literature Criticism : Allende to Jiménez (1994), p. 298