What happens after the Meryton Assembly?

Mr. Bennet and Sir William Lucas had paid calls on Bingley. He had returned the call to Mr. Bennet, but had not met the Bennet girls. It was at the Meryton assembly that all the neighborhood had their first sight of the Netherfield party. Mr. Bingley makes himself generally agreeable and dances readily with many partners, including Charlotte and Maria Lucas, Jane (twice) and Elizabeth Bennet. Mr. Hurst, husband of one of Bingley's sisters, is rather dull and uninteresting, as is his wife. Miss Bingley, the eldest sister, is elegant and fashionable but reserved. Mr. Darcy, though initially admired, falls into general disapproval because he is too aloof and proud to converse or to dance with anyone outside his own party, in contrast to Mr. Bingley.
While the text says that "Mr. Bingley had soon made himself acquainted with all the principal people in the room," this does not mean that Mr. Bingley met all five of Mrs. Bennet daughters, though he probably met Mrs. Bennet herself.
Since Mr. Bingley danced with Jane twice, "and the two fifth with Jane again," and spoke of her to Darcy as being "the most beautiful creature I ever beheld," it is understandable that, in a culture that valued marriage, their romance developed quickly. It is true that Darcy and the Bingley sisters were not pleased, but their reasons had nothing to do with Jane's "lower status," or lower social class, because, as they knew, Jane's social class was equal to theirs. What was not equal to theirs was the amount of wealth Mr. Bennet had (he squandered his wealth because he erroneously believed he would produce a son and heir to rebuild his estate), and what may not have been acceptable to them was the size of the dowry Jane was entitled to. Also, Mrs. Bennet's boasting and rudeness, her unpolished and arrogantly proud manners, were not tolerable to any but easy-tempered Bingley.
Mrs. Bennet is delighted with Mr. Bingley's attentions to Jane. She even plots to trap Jane at Netherfield by having her ride there in inclement weather, in response to an invitation from Miss Bingley. Her motive is to keep Jane there until Mr. Bingley returns from London the next day. Her plan works out, rainstorm and all, except that Jane develops a dangerous cold as a result (this turns out well for Darcy as Elizabeth comes to Jane's aid allowing him to be entranced by her "complexion"). Jane stays until Bingley returns, but is confined to bed with a high fever and comes under the care of an apothecary.
An unintentional result of Mrs. Bennet's plan, is that Elizabeth's presence spurs Darcy's reconsideration of her and his newfound attraction to her. Elizabeth takes alarm at the note Jane sends regarding her illness, reading much more meaning into it than their mother does, and walks immediately to Netherfield to ascertain for herself the condition Jane is in.
When Elizabeth enters the Netherfield front door, she is shown by the servant into the "breakfast-parlour, where all but Jane were assembled, and where her appearance created a great deal of surprise" because of her dirtied and invigorated appearance.
Elizabeth [walked] crossing field after field at a quick pace, jumping over stiles and springing over puddles with impatient activity, and finding herself at last within view of the house, with weary ankles, dirty stockings, and a face glowing with the warmth of exercise.
While Darcy was concerned that Elizabeth's risk and over-exertion were not called for in the circumstances, he was also struck with "admiration of the brilliancy which exercise had given to her complexion." As the days of Jane's illness went by and Darcy had more and more conversations in which Elizabeth, as well as the Bingley sisters, took part, his admiration for her "fine eyes," initiated at Sir William Lucas's earlier impromptu dance party, expanded into admiration for her "sweetness and archness." He is led to realize that had it not been for the Bennet's inferior family connections, he might be in danger of feelings of love for her.
Darcy had never been so bewitched by any woman as he was by her. He really believed, that were it not for the inferiority of her connections, he should be in some danger. ... He began to feel the danger of paying Elizabeth too much attention.
It must be stressed that while inferior family connections—the Gardner grandfather having been a lawyer, Mr. Gardner being in business, Mr. Philips being a Meryton lawyer—may also mean inferior degrees of wealth, it is not necessarily so. Take the Bingleys, newly made wealth for example: they may be presumed to still have inferior connections themselves, though they are wealthy enough to move to the upper class. It must be clearly understood that it is not correct to change Darcy's statement that Elizabeth's "inferiority of ... connections" sways him against her so that it reads that Elizabeth's economic inferiority is what sways him against her. While the two may go hand-in-hand, what bothers Darcy are the connections the Bennets have with inferior people, using proud and boastful Mrs. Bennet as his standard of judgement against their connections.