Well checking the backstory in the fan box, on top of bullying him normally she made him mast*rbate in front of their classmates while she was recording. Blackmailing with uploading the video to the internet should he tell anyone he was being bullied by her and her friend group.
At this rate, i will accept the ending where they do a double suicide. Girl happy that she wont let the guy die alone and the guy happy that the person he hates the most dies. Hey i kinda can see a form of love there albeit crooked as it can be.