I really don't think they made her a terrible person, and more like a complex girl who thought she was doing what was best for him (even thought it was wrong). i think it ties into Japanese culture and how everyone is forced to be collective and similar to each other through looks as well, that even when he was growing up people would whisper that he was being beaten at home. Wouldnt she want to hide something like that? Especially at an age where judgement hurts a lot more?
I definitely think it's easy to think, 'shes just a terrible person' but not the fact that shes a teenager, and that's actually a more normal reaction than what usami showed. Usami was accepting because he understood what it was like to be slightly different in the culture that they live in, that it's not wrong to look or be a certain way. That he's been bullied before too for something he can't control.
To make the girl into a cannon fodder for their relationship and just see her as a "terrible girl" like in cliche BL, takes away from the fact that she is a representation of Japanese collectivism and how she's actually more common than we think. She's not terrible, just human. She learned from her mistakes and apologized and hopefully that can help some people reading this to not be so judgemental as well.

this was about to be a 5* for me but then they had to go and make the girl a terrible person as if bl stories didn't already have enough of that... i'm glad there was communication but the way she treated him just felt so forced in order to push the two boys together. it's a little upsetting but it's not something super horrible or anything, i'm just tired of seeing that trope. otherwise this was decent ^^