_____Swann is attempting to leave the party when the musicians begin a familiar piece:
And before Swann had time to understand, and say to himself: "It's the litte phrase from the sonata by Vinteuil; don't listen!" all his memories of the time when Odette was in love with him, which he had managed until now to keep out of sight in the deepest part of himself, deceived by this sudden beam of light from the time of love which they believed had returned, had awoken and flown swiftly back up to sing madly to him, with no pity for his present misfortune, the forgotten refrains of happiness.("Nessun maggior dolore / Che ricordarsi del tempo felice / Nella miseria.")
And so Proust (or "the narrator") launches into an examination of the nature of music, as an entity with a life of its own (just as Swann's memories have an autonomous life -- they believe that "the time of love ... had returned"). Swann feels that "the little phrase was addressing him, was talking to him in a low voice about Odette. For he no longer felt, as he once had, that the little phrase did not know him and Odette." In Swann's/Proust's/the narrator's formulation music "belonged to an order of supernatural creatures whom we have never seen." The composer (and the performer) is an "explorer of the invisible" who captures the creature.
The concert is also a turning point. "From this evening on, Swann realized that the feeling Odette had had for him would never return, that his hopes of happiness would never be realized now." But although he has resumed his study of Vermeer, and needs to travel to see some of the paintings he has under consideration, he can't bring himself to leave Paris.
One day he dreamed he was leaving for a year; leaning out the door of the railway car toward a young man on the platform who was saying good-bye to him, weeping. Swann tried to convince him to leave with him. The train began to move, his anxiety woke him, he remembered that he was not leaving, that he would see Odette that evening, the next day, and almost every day after.It's unclear here what significance needs to be attached to the fact that in the dream, the surrogate for Odette is a young man.
He has become so desperately entrapped in his infatuation that he wishes for her accidental death, likening himself to Mohammed II (the subject of a favorite painting by Bellini, whom Swann once found the narrator's friend Bloch resembled), "who, realizing that he had fallen madly in love with one of his wives, stabbed her in order ... to recover his independence of mind." Murder doesn't yet seem to be in Swann's repertoire, but "the dread ... of causing her to hate him, had vanished now that he had lost all hope of ever being loved by her."