Why is the question of adultery unresolved in Dom Casmurro?

The question of adultery in Dom Casmurro remains unresolved because the novel is a first-person narrative filtered entirely through the perspective of its protagonist, Bento Santiago.1

Machado de Assis crafted the work as a haunting journey into a mind warped by jealousy. Because the reader only has access to Bento’s subjective, unreliable account of his life and his suspicions regarding his wife, Capitu, there is no objective evidence provided to confirm or deny the alleged infidelity. By utilizing this indirect and cynical narrative style, Machado forces the reader to confront the ambiguity of the protagonist's perceptions rather than providing a definitive factual conclusion.1