The coffee cup scene is the one in chapter CXXXVI in which Bentinho prepares a coffee with poison to kill himself and, at the last instant, nearly gives it to his son. It is the moment when the suspicion against Capitu becomes an act.
It all begins the day before. On a Saturday, Bentinho buys a substance that the book does not name and feels, with death in his pocket, the joy of someone who has won the grand prize. That night he attends Othello and concludes that it was Capitu who should die. The next morning, he dissolves the poison in the coffee and plans to drink it, but postpones until his wife and son leave for Mass. Then Ezequiel enters the study shouting "Papa." Bentinho's first impulse is to rush to the coffee and drink it; the second, as he himself says, "was criminal": he holds the cup out to the boy. He draws back, kisses the boy's head and says: "No, no, I am not your father!"
Capitu enters shortly after and demands an explanation. Bentinho repeats that the boy is not his son and alludes to Escobar's love affairs without saying his name, and she replies that not even the dead escape his jealousy. Then come Escobar's photograph, the separation and the trip to Switzerland.