http://youtu.be/z76l53LukE8
That's what he thought happened but Jaime tells him that she wasn't actually a whore, meaning she did truly love him which added to his motivation to kill Tywin.
I've already said I'm not usually that bothered by changes from the books but they've already included the first half of this and it's something I felt that would have made the TV show even better, which is why I'm disappointed they left it out. However, like Paul says, the scene was 3 years ago so a lot of viewers would have probably forgot or been hazy on the story with Tysha, which is probably why they've left it out.