Darcy begins this proposal with romantic words, shrouded in disbelief at the thought of being in love with Elizabeth, someone who is well beneath him socially and certainly financially.  He metaphorically lunges at her in this clumsy proposal that sounds more like a confession of a long held secret illness, one that he cannot rid himself of and is desperate for a cure, than a real proposal based on the love he mentions in his lines.

"In vain have I struggled. It will not do. My feelings will not be repressed. You must allow me to tell you how ardently I admire and love you.'' (Austen)

If Elizabeth is at first startled, she is then made to feel sorry for this suffering man in front of her, which quickly turns to anger when she realizes that he is expecting her to say yes, actually to say yes rather quickly, considering all that she stands to gain in the marriage.

He is so offended by her rejection of him that he can barely keep his composure.  He is hurt, angry and stunned.

"And this,'' cried Darcy, as he walked with quick steps across the room, ``is your opinion of me! This is the estimation in which you hold me! I thank you for explaining it so fully. My faults, according to this calculation, are heavy indeed! But perhaps,'' added he, stopping in his walk, and turning towards her, ``these offences might have been overlooked, had not your pride been hurt by my honest confession of the scruples that had long prevented my forming any serious design" (Austen)

Elizabeth Bennet puts Fitzwilliam Darcy, rich, rich man, with a grand estate Pemberly, in his place, even though her family is in desperate need of a new home and she is very much in need of a husband and financial security.

Darcy, walks out declaring that he will not bother her again, but the reader knows that Elizabeth's feisty refusal has only inspired Darcy to find another way into this woman's heart.