wind in my hair, I was there

happy taywedding day to all those who celebrate

Elizabeth has never insulted him to his face before the first proposal, though, so he's definitely not gonna think she'll do that in their marriage. That's why he's so shocked when she does insult him in her rejection—she has never done it before.

Unlike the rest of the Bennets save Jane, Elizabeth is polite and follows social etiquette. She only skates on the line of impertinence in a way that simply comes off as playful banter and teasing. She openly disagrees with Darcy sometimes, but that is not the same thing as insulting him, and never does it to him in an overtly rude way. Even when she tells him his flaw is to hate everyone, I don't think that has to be read as an insult, just flirting, because he smiles at her when she says it and immediately afterwards thinks he was too attentive to her. To him in these moments, they're either just having a discussion or flirting, and at worst she seems annoyed with him a couple times, no big deal.

Now, Elizabeth herself does insult her manners at the end, but she's doing it in a playful self-deprecating flirty way, and Darcy obviously doesn't agree with her read of herself, nor do I:

“My beauty you had early withstood, and as for my manners—my behaviour to you was at least always bordering on the uncivil, and I never spoke to you without rather wishing to give you pain than not. Now, be sincere; did you admire me for my impertinence?” “For the liveliness of your mind I did.” “You may as well call it impertinence at once. It was very little less...

The only characters that think that Elizabeth has bad manners are Miss Bingley, Mrs. Hurst, and Lady Catherine, and we certainly can't take their reads as being fair ones!

In fact, not only does Elizabeth not insult Darcy, but there are times when Elizabeth actually says seemingly nice things about him in front of his face, such as when she calls him "a man of sense and education," says he is "all politeness," or comes to his defense when Mrs. Bennet starts insulting him at Netherfield during Jane's illness. Elizabeth also says things to him which seem very flirty, like when she turns down his offer to dance a reel in the cutest way possible.

So, to go back to your original question, OP, about what Darcy thought his marriage with Elizabeth would be like, he probably thought they would continue to have spirited discussions in which she sometimes disagreed with him and sometimes teased him, which sounds fun, and overall she would be affectionate to him because he's seen she has a loving heart toward her family, and thus everything would be unicorns and rainbows 💕

Which makes it sooo delicious when she turns him down and he gets to find out he was utterly wrong 😈