The heartbreak at th heart of Little Dorrit, and a sin to expiate

Two contrasting chapters nearing the mid-point in Charles Dickens's Little Dorrit (1855), as one chapter presents the sad news, to Arthur Clennom (the protagonist) that the woman, Pet (!), whom he is in love with - and whom he tries, comically, to convince himself that he does not love, as he imagines he wouldn't have a chance w/ her - comes to him and tells him she's in love w/ his odious rival: a match that Arthur knows will be horrible for Pet but also that all his hopes are dashed. He should have acted sooner, he should have been forthright, he should have for once taken a risk - and now he's like the singer of a million blues songs (e.g., You Don't Know Me),, a guy who deserved much better (and is likely to find true love, one imagines, somewhere over the next thousand pages). Another chapter harks back to the first chapter, when we meet a nasty guy on the verge of release from a French prison; now, on a typically Dickensian stormy night in London, the Frenchman shows up at the door of Arthur's mother's dingy house, talks his way into an audience w/ the nasty old woman, tries to ingratiate himself w/ her business agent, and hints that he's trying to rectify a great wrong done by the Clennom family, all mysterious to this point to readers - except that we know Arthur has a sense of a family sin that must be expiated, that he must discover and expiate - and we sense that somehow or other this sin and expiation must involve the eponymous Little (Amy) Dorrit, that a sense of guilty (or a need to keep LD close and dependent?) is what led Arthur's mother to take on LD as a seamstress.