I wonder if the time she considered herself 'abandoned' inevitably died, was the day Hinata's incarnation (as the grandma) died? Also this is going to be hard to explain now
Basically, Nagisa found a cat in a shrine but cannot adopt it because his grandma hate cat. The cat blame Nagisa for abandoning her. In a way, Hinata is responsible for the eventual dead of Sakuya.
@GodGinrai Sadao apparently had no other family than his grandmother, so when Hinata-chan died in her past life, he had to move away from her home to... somewhere else. He may have been moved out of the city at that point into a foster home, and only recently moved back. This means, unfortunately, that Hina-chan's death in her past life directly lead to Sakuya's death. I hope Sakuya doesn't make that realization and blame Hina-chan.
The official translations from Seven Seas have passed up the fan translations at this point. I found copies of them to try out, but only skimmed the volume past this one, as I much prefer the fan translations. (Hina-chan isn't Hina-chan without her dappes!) So I don't know exactly what happens here, but I did notice one thing that hints at how it goes. (It is a spoiler, so don't read if you don't want to be spoiled!):
Sakuya cuts her hair, as she has short hair in volume five. This suggests she gets over Nagisa/Sadao and loses her first love.
I hope she grows it back out, as she's a lot cuter with the long hair.
@Stickerparty Can you imagine just how insanely confused poor Sadao is at this point? He doesn't even know who Sakuya is, but she slaps him and starts crying.