I knew she was going to toss away the notebook, but I did expect her to burn it like the girl in the story did the painting, and then jump too.
It's tragic that Chihiro believes she doesn't deserves happiness. She always thinks she's hurting everyone. She apparently drove Kei off too long ago. Or at least forceably separated herself from her. She doesn't see that Renji has already seen the worst of it (one of her total collapses), has already felt terrible about it, and already been tortured by her when he flipped out at the sand castle. The difference is that Renji is hurt by how unfair life has been to Chihiro. He wants to bring her happiness, and he already came back for her. He's willing to endure the pain and suffering in order to make her happy, and be happy with her. In the light of her happiness, the pain means nothing to him.
I suppose if there is to be a happy ending, Renji will have to spend the next episode making her realize that.