I think so many of the problems with Robb and Cat on the show stem from the fact that D&D basically wrote themselves into a hole.
I understand why the aged the characters up. But this is troublesome in terms of Robb’s storyline, because so much of his character arc in the books is rooted in the fact that he is a young boy in way over his head. And – at least on some level – he knows he is in way over his head. At one point, he admits (paraphrasing) that he’s “messed up everything but the battles,” and he is willing to listen to Cat’s advice, even if he occasionally resents her for giving it. On the show, Robb is roughly twenty. Ned and Robert fought and won a rebellion at that age. Stannis held a castle under siege. By Westerosi standards, Robb is too old to be (believably) relying on his mother, so they’ve given him too much confidence and have him treating Cat like an interloper.
Also, his show storyline is all over the map, with Catelyn in tow. In the book, she releases Jaime at Riverrun while Robb is away, which makes the whole thing Edmure’s problem, and Cat basically makes it easy on him by confining herself to Hoster’s chambers until Robb returns. And when Robb does return, he is immediately willing to forgive her, because he also made a potentially politically disastrous mistake in his grief. Putting Cat on the road with him, and turning the Talisa arc into a thing where he actively pursues a relationship outside the Frey alliance changed the tone of everything. So, he treats Cat like a criminal, because why not.
I’m still really salty about it. And not just because I genuinely like Robb in the books. I hate what it’s doing to Cat as a character, because they are basically trying to turn her into someone to be pitied, which IS SO FAR FROM THE POINT I AM FOAMING AT THE MOUTH. One of the most heartbreaking things about the whole King in the North arc in the books is that Cat shows an amazing amount of strength. She just keeps soldiering on because Robb needs her, despite her personal losses and the fact that his kingdom is falling down around their ears.