Franz's circle of friends knows about his student-lover and his separated wife Marie-Claude. But no one knows about Sabina. Marie-Claude didn't want word to get out because Sabina was so much more beautiful than she.
Franz doesn't even have any mementos of Sabina after her departure. This makes him want to remain faithful to her. Even when he's with his student-lover, he's thinking of Sabina. Yet he doesn't feel he's doing wrong by his young lover; "he nourished the cult of Sabina more as religion than as love" (3.11.7).
His student-lover is young and has not yet developed her own musical motifs. She is grateful to take on Franz's. The only thing she doesn't adopt, indeed does not understand, is his love of countries occupied by the Russian empire.
Franz once takes her to a meeting on Geneva of Czech émigrés. Franz sees in the speaker a secret messenger, an intermediary between him and his goddess, Sabina.