If I try to analyze this more than I should as well like
@Kaarme , then I suspect her "acting" was an excuse or deflection. She DID think he was not only starting to hate her, but with her self-esteem, she probably thought he was already there. I don't know how quickly a depressed person's mood can swing, but I'm guessing she was already starting to calm down/feel relieved when he assured her that he wasn't angry with her (i.e. hate her).
I could be wrong though. Personally, I'm a bit on the opposite spectrum. I went through a long period as a NEET and during that time, in fact, even before it while I was in school, I could barely feel intense emotions beyond the fear of death. I got used to emulating emotions according to social contexts in school, like knowing when to/not to laugh (you know, the fake social laugh thing...), so seeing people in fiction suddenly switch gears like this (
especially when switching from what is known as a height of emotions) has always been, and perhaps a bit insensitive, strange and fantastical to me.