Daryll Delgado's short story "Preludes" is full of ambiguities and uncertainties. Delgado deliberately leaves the reader to surmise exactly how Nenita's husband died. We are told that Nenita took her husband back after his affairs and nursed him back to health when he was ill. We are also told that she bought poison, a packet of dried purple leaves, but that she never used it on her husband. It simply gave her "a very calming sense of power" to know that she had it.
It is possible that Nenita kills her husband after all. Delgado does not rule out this conclusion, despite the fact that she does not use the poison. However, it would be more in keeping with her character to conclude that she knows he will die and waits passively, doing nothing to save him. Just as her infidelities are imaginary fantasies about Willy Revillame, a celebrity on television, rather than the real-life affairs of her husband, so Nenita imagines killing her husband, whom she does not love, rather than actually doing the deed.
One might see it as a kind of justice that he is punished for his real unfaithfulness by a real death, while Nenita escapes unscathed for her imaginary adultery, but I believe such a reading of the story is excessively literal, at odds with the subtlety of Delgado's narration. This is a story about two ill-matched people who do not love one another, and the fact that Nenita's infidelities take place only in her mind seems merely a matter of timidity or lack of opportunity rather than anything more noble.