In the book tyrion never sends Shae away though he wants to for her protection. She just turns up at his trial and betrays him. For sure Tywin having her in his bed is to show his hypocrisy. Its never clear did she love Tyrion or was she just a whore. When she sees Tyrion she says my lion did you come to rescue me, and your father is a very dangerous man. But he kills her anyway. She never pulls a knife on Tyrion like in the show.
I did not think she was worthy of Tyrion’s love on the show. And I was not surprised that she betrayed him or that she used the knife in the fruit and cheese bowl, when Tyrion came upon her in his father’s bed. When she had told Tyrion, “I am your whore,” I think she was projecting that she would do anything for money.
I do wish Sansa would have spoken more kindly of Tyrion to her aunt and the council in the Vale. He never forced himself on her, despite the pressure, and Tyrion did show he was concerned for her when she was mourning for her family, and he did take his wedding vows seriously.
Now, it gets me back to how Arya scorned the Hound. I re-watched the scene again. You could see his lower jaw tremble, when he asked her to kill him, and the sound of his voice as she walked away, denying him a merciful death, the way it rang roughly, wounded by her heartlessness, echoing through the valley, was painful to hear.