Let's summarize here. Book-Robb is a boy of 15 (full of raging hormones); he took an injury at the Crag; he heard of his brothers's deaths and is grieving. During all that he is "comforted" by a woman in a moment of understandable weakness. After that happens, he feels honour-bound to marry her. Book-Robb is the son of Ned Stark, and just like Ned, he takes oaths and hononour seriously. He would have never deliberately broken his vow to the Freys like that, and when it does happen, he feels stupid and terrible and tries his hardest to make amends.
TV-Robb: is a man grown (I assume he's supposed to be 18-20?); he is not injured; he has not learned of Bran and Rickon's deaths and is not grieving. He's not in any sort of particular trouble. He even had his mother around to remind him of his duty and his oath to the Freys. Yet he's palling around with some sexy wench and clearly states he doesn't want to marry the Frey girl. He deliberately breaks his vow and doesn't even have second thoughts about it.
What made Robb sympathetic was because he was so much like Ned, and took his oath and his honour so seriously, and he was young and naive, and he actually married Jeyne because of his Ned-like honour as a Stark. There is none, and absolutely none of that in his story with Talissa. Not only is the story contrary to the spirit of the novel, but even judged by its own merit as TV, it's bad. It's a clichéd Hollywood romance with little believability to it. And it takes away a lot of the tragedy of the Red Wedding since Robb pretty much has it coming. Personally the Red Wedding made me upset because of Catelyn's suffering (losing her "last" son) and death more than Robb's death, but by giving more attention to Robb, the TV series could have changed that. Well, so much for that...







