For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Mr. Darcy insults Elizabeth in range of her hearing, then starts falling in love with her.
Mr. Darcy proposes and gets rejected. He gives Elizabeth a letter that throws many of her assumptions and beliefs into question.
Darcy's proposal, round two – he's accepted.