After breakfast, as Harry is preparing to leave with Lorsborne, Harry pulls Oliver aside and asks him a favor: that Oliver might write to Harry every day, reporting on how things go in the house, and on how Mrs. Maylie and Rose are doing. Oliver agrees to do so. As Harry and Lorsborne departs, Rose sees that Harry is happy (because Oliver has agreed to write to him with news of Rose); Rose interprets this happiness as relief that Harry does not have to marry Rose after all, and Rose, quietly, is sad at the prospect of perhaps not marrying Harry after all, although, of course, in the chapter before she said no to this proposal of marriage.
This is an interesting case in the novel—a plot point that appears to have been placed by Dickens, but which seems not to be followed up on in the remainder of the text. Harry does need to receive information about the Maylie family, as he is far away during most of the events that occur in the last quarter of the novel, but it seems that Dickens probably intended to make more of this correspondence with Oliver than he in fact ended up doing. These sorts of blips in continuity are common in novels written serially, in which the writer was writing just slightly ahead of the publication of each chapter.