When we think about plot, the last stage of any plot is the resolution. This is where the conflict that has driven the story throughout is finally brought to some sort of conclusion, as the term "resolution" implies. It is therefore important to think about what the conflict of a novel is in order to comment effectively on the story's resolution.
In this text, the conflict is clearly between society and following its norms and rebellion and following our own selfish desires. We have seen the epitome of rebellion in the figure of Dean. Dean is a character who Sal is immediately attracted to precisely because he does what he wants and seems to be such a liberated character, unrestricted by the norms of society. However, when Dean abandons Sal when he needs him during his sickness in Mexico City to pursue his own selfish desires, Sal's view of Dean begins to change slowly but surely.
The resolution then features the final meeting between Dean and Sal. Sal has already begun to change. He has found his true love and is going to settle down. However, Dean vists them unexpectedly and reveals his chaotic love life. Sal wants Remi Boncoeur to meet Dean, but Remi does everythign he can to avoid spending time with Dean, and Sal is forced to go to the concert that they planned to go to and leaving Dean standing in the freezing cold. They never meet again, but he does remember Dean for his youthful, exuberant spirit and the way that he seemed to capture a golden age of freedom and liberated living. The only thing that is certain in this world, Sal reflects, is "the forlorn rags of growing old."