I love this story. None of it intends to paint anyone in a perfect light, it's about how imperfect, troubled and fucked everyone is and their also imperfect attempts to deal with it. It's very real as others have said.
If it were real life I'd say that everyone here definitely needs therapy and a half. But since it's a story that is intentionally dark, I'm all for Aya x Sei even while it's unhealthy (and the teacher x student thing is obviously uncomfortable), it seems they've been slowly making changes in each other for the better, and are direct responses to what they both hate about themselves. And their dynamic is just so good. Some of those scenes where both Aya and Sei were briefly vulnerable and honest to each other made me genuinely feel things. I'm not sure if they'll end up together or even if they should end up together, but I'll be enjoying the trainwreck there.
I can't understand rooting for Haruki at all though. I personally find her the least believable and likeable character. It's quite funny and interesting how split the opinions about her is on here. Though Yoru I also find a bit confusing (she pretty tho), it's hard to say whether she ended up being a victim of/twisted due to Sei's obsessive mindset or just as bad/to blame through her constantly stringing Sei along and generally being unfaithful and complacent. Or maybe it's just both. Either way, it was definitely too far gone and complicated and I do think it was not a problem they could 'solve' anymore, so this chapter seemed to be the best way for it to go, really.
Considering Sei and Aya's relationship was so heavily based around Yoru still, I'm curious to see what happens to it now if Sei starts to finally move on.