To return to a quote from last time, having left this for a few months:

Poets claim that we recapture for a moment the self that we were long ago when we enter some house or garden in which we used to live in our youth. But these are most hazardous pilgrimages, which end as often in disappointment as in success.

I don’t know if Proust is referring to Wordsworth here, but it’s the Wordsworth of Tintern Abbey that this passage brings up for me, and how he implies an almost inviolate integrity of the self and its memories, one which Proust has already systematically destroyed in Swann’s Way and is now extending to social networks themselves. Very little happens in the entirety of The Guermantes Way; the main plot points are his grandmother’s death and his eventual disenchantment with the Guermantes (on this point, Marcel is a lot more patient than I would have been), and the final revelation at the end of the volume, which I’ll mention later. The main function of the book is to establish how tenuous Marcel’s images of people are, and how the brightest things that he saw earlier have faded or have been completely replaced.
Saint-Loup was one of the most likable characters in Within a Budding Grove, and he’s still likable here: his basic goodness, politeness, and generosity contrast favorably with the pettiness and amorality of most of the other high society characters. But he is a Guermantes, and to the extent that the book is an indictment of the Guermantes way (which, believe me, it is), Saint-Loup is included. He still comes off as the best of the lot, not least for his steadfast anti-Dreyfusism, which appears to come from a genuine moral stance rather than simple trendiness. Yet the conclusion on him is, I think, that his inability to be critical damns him to complicity.
His good side is on display at a party:

It occurred to me on one of these evenings to tell a mildly amusing story about Mme Blandais, but I stopped at once, remembering that Saint-Loup knew it already, and that when I had started to tell it to him the day after my arrival he had interrupted me with: “You told me that before, at Balbec.” I was surprised, therefore, to find him begging me to go on and assuring me that he did not know the story and that it would amuse him immensely…And throughout the story he kept his feverish and enraptured gaze fixed alternately on myself and on his friends. I realized only after I had finished, amid general laughter, that it had struck him that this story would give his comrades a good idea of my wit, and that it was for this reason that he had pretended nto to know it. Such is the stuff of friendship. (103)

The story about Mme Blandais is never mentioned; it’s not important. Marcel’s affection for Saint-Loup here is nearly unmatched. So it comes as a disappointment shortly after Saint-Loup appropriates one of Marcel’s trite conclusions about the world:

I had reckoned without the reverse side of Robert’s cordial admiration for myself and certain other people. That admiration was complemented by so an entire an assimilation of their ideas that after a day or two, he would have completely forgotten that those ideas were not his own. And so, in the matter of my modest thesis, Saint-Loup, for all the world as though it had always dwelt in his own brain, and though I was merely poaching on his preserves, felt it incumbent upon him to greet my discovery with warm approval…
He paused for a moment, with the satisfied smile of one who had digested his dinner, dropped his monocle, and, fixing me with a gimlet-like stare, said to me challengingly:
“All men with similar ideas are alike.”
No doubt he had completely for gotten that I myself had said to him only a few days earlier what on the other hand he had remembered so well. (119)

This gesture is as significant as the last. Saint-Loup is not a malicious person, but he possesses a certain thoughtlessness that, while generating moments of friendship, just as soon alienates Marcel when Saint-Loup treats those around him as sources from which to draw elaborations of his personality. Not that Saint-Loup himself doesn’t suffer. When he gets involved with Rachel, the prostitute that Marcel and Bloch met in the previous volume, he is completely oblivious to her nature:

Robert was ignorant of almost all the infidelities of his mistress, and tormented himself over what were mere nothings compared with the real life of Rachel, a life which began every day only after he had left her. He was ignorant of almost all these infidelities. One could have told him of them without shaking his confidence in Rachel. For it is a charming law of nature, which manifests itself in the heart of the most complex social organisms, that we live in perfect ignorance of those we love. (292)

Proust generalizes Saint-Loup’s behavior to the world at large, but Saint-Loup’s is a particularly extreme case, somewhat like that of Swann but different in that Saint-Loup does not seem to go through the extreme mood swings that Swann did with Odette. He is merely happily oblivious, and pleased to defend that attitude. And for Proust at least, it blunts Saint-Loup’s virtue.