Marcel is hardly ever so miserable as when he experiences friendship. It is at once the promise of the end of his loneliness and the betrayal of his self.
…I told myself that I had a good friend, that a good friend was a rare thing, and I savoured, when I felt myself surrounded by assets that were difficult to acquire, what was precisely the opposite of the pleasure that was natural to me, the opposite of the leisure of having extracted from myself and brought to light something that was hidden in my inner darkness. If I had spent two or three hours in conversation with Saint-Loup and he had expressed his admiration of what I had said to him, I felt a sort of remorse, or regret, or weariness at not having remained alone and settled down to work at last. (II,431)
Leaving aside the feeling of wasting his time instead of being a creative writer, which was an empty concern, he felt guilt because he was in a sense using Saint-Loup, using him as creative fuel.
He was no more than an object the properties of which, in my musings, I sought to explore. The discovery in him of the pre-existent, this immemorial being, this aristocrat who was precisely what Robert aspired not to be, gave me intense joy, but a joy of the mind rather than the feelings. (II,432)
And Saint-Loup explains why Marcel is so attracted to the aristocracy. At their best, they simple are, without aspiration, noble.
…I sense in it above all the certainty or the illusion in the minds of those great lords of being “better than other people,” thanks to which they had not been able to hand down to Saint-Loup that anxiety to show that one is “just as good as the next man,” that dread of seeming too assiduous of which he was indeed wholly innocent and which mars with so much stiffness and awkwardness the most sincere plebeian civility. Sometimes I reproached myself for thus taking pleasure in considering my friend as a work of art, that is to say in regarding the play of all the parts of his being as harmoniously ordered by a general idea from which they depended but of which he was unaware and which consequently added nothing to his own qualities, to that personal value, intellectual and moral, which he prized so highly. (II,431)