The conversation between Elizabeth and Darcy begins when she thanks him for bailing her sister out, and has to explain that her aunt didn't betray his confidence without her direct application.
"If you will thank me," he replied, "let it be for yourself alone. That the wish of giving happiness to you might add force to the other inducements which led me on, I shall not attempt to deny. But your family owe me nothing. Much as I respect them, I believe I thought only of you."I should note that while I generally have lots of negative things to say about the choices made in the 2005 production of Pride & Prejudice, I differ from many Janeites in defending the lovely lines spoken by Matthew MacFadyen-as-Darcy during the proposal: "You have bewitched me, body and soul," and his stammering over the words "I love you" and such are completely within the purview, I believe, of "he expressed himself on the occasion as sensibly and as warmly as a man violently in love can be supposed to do." Also, I love Matthew MacFadyen's delivery. And voice. And general appearance. But still, the lines are defensible, in my opinion, even if his appearance sans cravat and with his shirt open practically to his navel and her running about in her nightrail or whatever is not.
Elizabeth was too much embarrassed to say a word. After a short pause, her companion added, "You are too generous to trifle with me. If your feelings are still what they were last April, tell me so at once. My affections and wishes are unchanged, but one word from you will silence me on this subject for ever."
Elizabeth, feeling all the more than common awkwardness and anxiety of his situation, now forced herself to speak; and immediately, though not very fluently, gave him to understand that her sentiments had undergone so material a change, since the period to which he alluded, as to make her receive with gratitude and pleasure his present assurances. The happiness which this reply produced, was such as he had probably never felt before; and he expressed himself on the occasion as sensibly and as warmly as a man violently in love can be supposed to do. Had Elizabeth been able to encounter his eye, she might have seen how well the expression of heartfelt delight, diffused over his face, became him; but, though she could not look, she could listen, and he told her of feelings, which, in proving of what importance she was to him, made his affection every moment more valuable.
But I digress.
Turns out that Lady Catherine did indeed pay Darcy a call in London, only instead of talking him out proposing, her description of Lizzy's behavior made him think he had a chance at succeeding in a proposal.
"It taught me to hope," said he, "as I had scarcely ever allowed myself to hope before. I knew enough of your disposition to be certain that, had you been absolutely, irrevocably decided against me, you would have acknowledged it to Lady Catherine, frankly and openly."There follows a lot of "I was wrong"/"No, I was wrong" conversation and discussion of Darcy's letter and Lizzy's visit to Pemberley and Bingley's engagement to Jane it's all adorable and they are happy and get back to Longbourn and . . . we are left hanging as to what happens next. But I will tell you that if you haven't read the book before, it's funny.
Elizabeth coloured and laughed as she replied, "Yes, you know enough of my frankness to believe me capable of that. After abusing you so abominably to your face, I could have no scruple in abusing you to all your relations."
Aaaand . . . here's the scene from the 1995 BBC production: