Omg couldn't have said it better XD
Definitely felt the same way like you when I first read this manhwa
I recommend rereading it
It's one of those stories you read at first and have an face value opinion about it since you weren't expecting that from a webtoon
Sometimes you gotta analysis it too but there are people in the community who love this manhwa they share their own analysis on it
It might help you understand or like the story and characters more
(I've reread it like 5+ times and always learning or noticing something new)
Oh and also you seem pretty on point with your own suspicions of mental illness of the characters
I'm not for one who likes to "diagnose" or HC mental illnesses onto characters but I heard a lot of people agree Cirrus has BPD
Idk about Skylar but I heard people's theory is that he's is getting treated for PTSD
Hope that helps with your own analysis ^^
Neat yeah you're right. Both on Skylar maybe having PTSD and the fact that it's a little weird to HC people with mental illness. Especially since there are real people who deal with these conditions that are not characters in abusive relationships, don't act out violently, and can FRIGGIN communicate!!! (I'm not mad ). But also what is the DSM5 but a list of 2D personality traits meant to be prescribed as labels to explain the mental state of someone to make it easier for doctors and psychologists? (Don't answer that I'm indeed bonkers)
Also weird reference/connection but when Skylar went went "Maybe you could date me?" To Cirrus it gave me direct flashbacks to SAO Abridged when the main character after having sex for the first time asks his friend if she wants to get married. And that's my weird reference for today.

I think it's very funny that if the MCs are probably the most mentally unstable bitches know to their school. (mental illness isn't what makes their relationship so unhealthy it's mostly miscommunication and lack of understanding) I feel like if the friend group finds out their dating the most the friends would do is be like "Oh shit we're fucked cause you bitches crazy" not "what? Gay people?!? You?!?"
Also I personally think Cirrus has BPD and idk what meds Skyler was taking at the beginning but he might be bipolar? Or he has severe anxiety or OCD or even all of them. It's kinda interesting that it's not the mental illness making them so unhealthy as much as it's them being bad at love coupled with mental illness exacerbating both.
Anyways the way they are so toxic to each other in such an imaginable way (they're characters it's not realistic but I can imagine myself as them) it kinda makes all the sweet parts fall flat... like where did all this chemistry come from without build up? But I am intrigued.