The book does not show Sofia yielding to Rubião or to anyone. What it presents are two declarations of love that she hears, a suspicion that the narrator dispels, and a doctor's guess that the book does not confirm.
Rubião is the one who declares desire. In the garden of Santa Teresa, he holds Sofia's hand and loosens it only when she begs: "Oh, don't break my fingers!" She tells everything to her husband and says the best course is to cut off relations, gradually or all at once. Later, Rubião hears from a coachman a story about a lady in a veil and finds a letter in her handwriting to Carlos Maria; the letter was the circular of a ladies' committee, and the narrator replies: "Slander of the reader and of Rubião, not of the poor coachman."
The one who declares himself to her is Carlos Maria, at a ball, with an hour at the beach that, according to the narrator, he invented. Sofia tries to forget, but the phrase returns like "a stubborn musical phrase," and later she dreams of him. On these thoughts the narrator says that the mind grows accustomed, and that there is always "a moral refuge in outward exemption, which is, in more explanatory terms, the body without stain." Earlier still, he had said that the door of her heart "was locked and double-locked."
At the end, Dr. Falcão, who barely knows her, tells Dona Fernanda that the two "loved each other" and then, alone, concludes: "that man was the lover of this man's wife." Dona Fernanda finds the suspicion "without foundation, absurd, implausible," and the coupé scene shows Sofia with aversion and fear of scandal. The book presents the doctor's conclusion as his suspicion, and leaves it so.