Just at the end of flash-back by seeng MC as a good guy
Thank you! I understand now. Re-read it, but the lead up + the last panel is subtle, but it's there!
After seeing that, it's become even more painful to know what she did behind Kaori's back and in her face. And Hidaka, who has taking inspiration from Kaori and thus has new-found vitality, hurts Kaori as well. Although, it's not clear why he falls in love with Yoshioka too.
Perhaps, this is the author exploring writing ideas: What if you give trashy people a sad backstory? How will the audience receive them? Lol jk. But it's a breath of fresh air to see the depth of characters compared to most stories these days. I can already see the author does not like to leave things open-ended and I'm sure we'll get our answers.