As i sadly don't remember the first 3 instance where the ring didn't appear, i don't point the finger at Nishina, but as you said, her face and her words have too much of an impact to not have any meaning behind. That's why i believed it was more likely because he "surrendered to the darkness" he spoke of and was being a prick...but that was considering both the words of Nishina and the fact that i don't remember the previous 3 cases. Now that you tell me that those 3 were truly liked/loved mc, my theory loses its base and all that is left for me is to wait and see lul