Chapter 31 really gives us an idea of how taken with Lizzy Col. Fitzwilliam is. ("Mrs. Collins's pretty friend had moreover caught his fancy very much.") It seems Mr. Darcy took notice of this as well. ("His eyes had been soon and repeatedly turned towards them with a look of curiosity") Is it possible Darcy's proposal was spurred on by jealousy of his cousin's attentions to Elizabeth?
Also, do you think, if he had been financially independent, Col. Fitzwilliam would have made an offer to Lizzy? He doesn't seem to mind her low connections. Would she have accepted?