Out of all the testimony in his trial, it was clear that Shae's stunned him the most, to the point where he was pleading for her to stop. And she didn't.

His resentment towards his father is deep seated and has been in place for a long, long time. But he had genuine (dare I say it) love for Shae, and his insistence on sending her away wasn't a betrayal but was for her safety. He still loved her when his trial started, but that ended when she opened her mouth.

Then finding her in Tywin's *bed*?!? Come on.