I think they try to point out that he switches so fast because one, he already liked him already. And two, after being left alone in the cave for a day, he believes dragosh is leaving him for good and considers that keeping dragosh with him is more important than his anger towards being left alone for 5 years and the possibility that dragosh's feelings is due to mental illness from no human contact during that time.
Though I agree that the author didn't do a really good job at portraying the switch in feelings.
Idk... It feels odd that everytime they have sex, ivo dreams of something odd. Its almost as if ivo isn't completely human too, and that ivo-looking spirite-looking thing might not be just a spirit-looking thing afterall.
It's surprising how in the first moment he is like "i won't forgive you, how could you fuck me, bla bla..." and in the next moment out of the blue he is like "I'm so lovey - dovey, fuck me and bla bla"... It's so sudden. I'm frustrated and confused...