_____Swann has gone nuts. Even if we hadn't been alerted to the unfortunate outcome of his relationship with Odette earlier in the novel, it would be quite apparent by now that it can't end well. But there's no talking him out of it, even with warnings that she's more interested in his social status or his money. As he sees it, those things will only bind her to him the more: "self-interest ... would prevent the day ever coming when she would be tempted to stop seeing him." A "dilettante of immaterial sensations," he regards Odette as worth the price:
as we observe that people who are uncertain whether the sight of the sea and the sound of the waves are delightful convince themselves of it and also of the exceptional quality and disinterest of their own taste, by paying a hundred francs a day for a hotel room that allows them to experience that sight and that sound.
His "mental laziness" deters him from investigating her reputation as a "kept woman," and his behavior begins to attract comment like that of the Princesse des Laumes, whose dinner party he leaves early so as to meet Odette: "Really, if Swann were thirty years older and had bladder trouble, one would excuse him for running off like that. But the fact is he doesn't care what people think." Indeed, he's pleased when Odette reveals to the Verdurins and the "little set" that Swann will be seeing her at home later.
Moreover, the depth of his obsession is revealed when, after Odette pleads a headache, meaning "no cattleyas tonight," he sneaks back to her house later and, seeing a light at what he thinks is her window, he fancies that she is entertaining a lover there. In fact, it fills him with a perverse, almost masochistic, joy.
And yet he was glad he had come: the torment that had forced him to leave his house had become less acute as it became less vague, now that Odette's other life, of which he had had, back then, a sudden helpless suspicion, was now in his grasp.... And perhaps, what he was feeling at this moment, which was almost pleasant, was also something different from the assuaging of a doubt and a distress; it was a pleasure in knowledge.
Characteristically, Swann intellectualizes his obsession:
[T]he curiosity he now felt awakening in him concerning the smallest occupations of this woman, was the same curiosity he had once had about History. And all these things that would have shamed him up to now, such as spying, tonight, outside a window, tomorrow perhaps, for all he knew, cleverly inducing neutral people to speak, bribing servants, listening at doors, now seemed to him to be, fully as much as were the deciphering of texts, the weighing of evidence, and the interpretation of old monuments, merely methods of scientific investigation with a real value and appropriate to a search for the truth.
Of course, this "scientific investigation" ends in farce, when he knocks on the window and discovers that what he thought was her room is actually in the house next door.
At this point, Swann's love has turned to neurosis, and however he might try to shut out the embarrassment of this misstep, "To wish not to think about it was still to think about it, still to suffer from it." And "every pleasure he enjoyed with her, ... he knew that a moment later, ... would supply new instruments for torturing him."
This section ends with a further unmasking of the "real" Odette, the woman who takes pleasure in Forcheville's cruelty to his brother-in-law, Saniette, and casts "him a glance of complicity in evil." It's an expression that tortures Swann.