Colonel Fitzwilliam is a younger son of Mr. Darcy's uncle, a lord, and so he is not entitled to inherit much because the family estate will pass on to his older brother. Further, at Lady Catherine's estate, the Colonel actually tells Elizabeth, "'A younger son, you know, must be inured to self-denial and dependence.'" Now, Elizabeth playfully questions how much this son of an earl can really have been denied or been forced to deny himself, and the Colonel admits that he really has not experienced much by way of financial hardships, but he does say, "'Younger sons cannot marry where they like.'" Unless, of course, Elizabeth reminds him, they fall in love with women who have fortunes of their own; she, of course, does not have such a fortune, and so this means they would not be considered a good match.
She refuses Mr. Darcy's proposal of marriage because she does not like him, and, moreover, she learns from Colonel William that Darcy purposely kept Bingley from pursuing his interest in her sister, Jane. The Colonel tells her that, apparently, "'There were some very strong objections against the lady'" (Jane Bennet, Elizabeth's older sister). Moreover, Elizabeth still believes Mr. Wickham's story about his dealings with Darcy and Darcy's alleged unjust behavior toward him. She thinks Darcy is a terrible person: arrogant and even cruel.