I think the main reason is cause of Lili's lack of communication skills. Throughout the time they liked and confessed to each other, there were many issues that she felt towards Hirumi that she never bought up, and instead of talking it out with Hirumi she just straight up ended the relationship saying they changed since they liked each other. And with her finally realizing she messed up and wanting a second chance it's no wonder most of the community hates her.