To explain it AGAIN: MC confronts his ex bully in episode 3 and - legitimately - demands answers. He gets them from her and we learn that her mother coerced her into it. In the further course we learn, not the MC, that this stemmed from the fact that MC's mother married his father, for whom she ( bullies mother - I'm bad with names) had feelings herself. MCs mother is about the current situation quite in the picture (state episode 3) and is also with one of the friends of his bully in contact, said friend has feelings for our MC, but can not show them openly to help her friend so from her situation.
To cut a long story short, the problem is not the girl herself but her mother. This has nothing to do with being a wimp, but with empathy.