I don’t have a great deal to say about the girls of Within a Budding Grove. Young Marcel’s impressions of them have as much to do with what he is looking for at that point in his life as with their individual personalities, and so he draws them coarsely and simply. Albertine is obnoxious, Andree is smart, and so on…it doesn’t make them unbelievable, but it places as much weight on Marcel’s impressions as there was on Swann’s fantasies of Odette in Swann’s Way.
The process repeats between Marcel and Albertine as it did with Marcel and Gilberte and Swann and Odette. After he first sees her:

Since my first sight of Albertine I had thought about her endlessly, I had carried on with what I called by her name an interminable inner dialogue in which I made her question and answer, think and act, and in the infinite series of imaginary Albertines who followed one after the other in my fancy hour by hour, the real Albertine, glimpsed on the beach, figured only at the head, just as the actress who “creates” a role, the star, appears, out of a long series of performances, in the first few alone. (917)

Albertine’s real presence, which is hardly overwhelming or even likable, eliminates a lot of his dreams, yet they have no deterrent effect on Marcel. On the contrary, he takes pleasure in the trivial discussions and cruelties of the girls, yet here is Proust talking about the loss of his rich image of Albertine:

As I drew closer to the girl and began to know her better, this knowledge developed by a process of subtraction, each constituent of imagination and desire giving place to a notion which was worth infinitely less. (933)

Proust’s analysis becomes so kaleidoscopic that it all but overshadows the main climax of the action, when Marcel makes a physical advance on Albertine and is rejected because she’s not that kind of girl. It’s meant as an indication of how Marcel’s own image of Albertine could not predict how he would act around her, nor did her own past actions and appearances give a foreclosed prediction of how she would react. Yet the moment-by-moment relativism is pushed to the point where this significant plot point recedes instantly, as, it is implied, Marcel retreats into his head.
His reaction after his advances are rebuffed is not that of the more emotional Swann, but detached reconsideration:

It was perhaps because they were so diverse, the persons whom I used to contemplate in her at this period, that later I developed the habit of becoming myself a different person, according to the particular Albertine to whom my thoughts had turned; a jealous, an indifferent, a voluptuous, a melancholy, a frenzied person, created anew not merely by the accident of the particular memory that had risen to the surface, but in proportion also to the strength of the belief that was lent to the support of one and the same memory by the varying manner in which I appreciated it. For this was the point to which I invariably had to return, to those beliefs which for most of the time occupy our souls unbeknownst to us, but which for all that are of more importance to our happiness than is the person whom we see, for it is through them that we see him, it is they that impart his momentary grandeur to the person seen. To be quite accurate, I ought to give a different name to each of the selves who subsequently thought about Albertine; I ought still more to give a different name to each of the Albertines who appeared before me, never the same, like those sees that succeeded one another and against which, a nymph likewise, she was silhouetted. (1010)

And it’s shortly after that note of disintegration that the second volume ends. Albertine is reduced to a specter, and everything that has just passed is the product of a character who is about to change, with his return to Paris. All that has gone on with Saint-Loup and Bloch, with Francoise and his grandmother, and with the young women, is left behind, as is the environment and the persona of Marcel that participated in creating the situations.
Again, what’s surprising is how subtly this despair and nostalgia creeps in, as well as the suggestion that attempting to hang on to those moments and recreate their circumstances that causes the deepest unhappiness. Superficially, he leaves Balbec peacefully, but the accumulating misery as he loses all that he gains, and as his later self in turn contextualizes it as though it were a dead specimen, gradually builds up into a terminal melancholy leavened only by the beautiful prose descriptions of past images.
That’s about it. While Swann’s Way ended with an inexplicable shocker revelation, Within a Budding Grove ends at the point where nothing could come as a shock any longer because everything is up for renegotiation. It’s not an auspicious point from which to launch 2000 more pages, and The Guermantes Way does retreat from these extremes in its early pages (what other choice was there?), but still, Proust’s terms from this vantage point look very bleak.