Well, in this kind of toxic relationship obsession and revenge are just one step away. Besides the uke was just beyond breaking point and just spouting whatever, he only reacted surprised because he probably hadn't expected the emperor to understand even half of it, let alone be able to reply in such a way that would mean that he (the emperor) has finally also regained his past life memories.
I agree for most of the part with u except ur first sentence. "Toxic", "obsessive" or "revenge". Even if u mix the first two. The last two r rather far away to mix. The emperor's behavior doesn't contain a hint of revenge idk how the guy even thought that. But it's all too obsessive. Remember the time the emperor said that the uke became the worst drug for him, he actually himself must not be in a psychologically stable state to make decisions and that is why did all those things.
Damn I thought this uke at least knew that the emperor was obsessed with him but now it seems he thought it all was revenge.