Why is sydney carton so sad and upset near the end of chapter 5?

Sydney Carton is sad and upset at the end of Chapter 5 of "A Tale of Two Cities" because he sees how wasted and dissolute his life has become compared to the idealism and purpose of those around him, especially Lucie Manette and Charles Darnay. He realizes that he is a self-destructive and unfulfilled man, leading him to despair.