nine2006

https://www.mangago.me/home/mangalist/3934504/

Boundary of delusion (seme is exhibiting concerning behaviour from the start and it only gets worse, tho this one's a little different and might not fit your description entirely you'll have to decide for yourself)

Die in my arms (uke is literally insane but we love that for him and his pathetic seme, this is a huge recommend from me)

Blind Play or 16647 Game And Reality. You are gonna love these

thanks for your rec but i’ve read that and i’m a hater .p

thanks i’ll check these out

thank you

Sad:
Lucky Letter

all of harada’s work (yatamomo, sumomo, nii-chan, color recipe n stuff), fruit of the tongue, no reason, black mirror, into the rose garden, the warehouse, missing love, adam’s rib, pufferfish and dolphins, non zero sum, sheep mask, red mansion, the ghost gate, blind play,

Idk what u consider classic so I'm just gonna chuck in a variety. Most of these r mangas as a heads up.

https://www.mangago.me/read-manga/my_hyung_s_lover/ (manhwa, psychological, kind of fucked up but in an interesting way, falls off towards the end)

https://www.mangago.me/read-manga/sensei_kowai_hanashi_shimasenka/ (manga, horror, fucked up bc it's student x teacher + iirc the student is kind of coercive)

https://www.mangago.me/read-manga/nemureru_tsuki/ (manga, this one is sooo good if u ignore one thing, bittersweet/ sad end, also kind of horror, v unfortunate case of incest, cousin x cousin, but that makes it fit ur criteria lol)

https://www.mangago.me/read-manga/ashtray/ (manhwa, just plain fucked up in a bad way, I'd categorise this as just rape and torture porn ngl)

https://www.mangago.me/read-manga/zankyou/ (manga, not labelled as a bl but there is a gay relationship, a bit fucked up and also sad ending, seinen)

https://www.mangago.me/read-manga/lonely_to_organdy/ (manga, Ghost x human, sad ending)

https://www.mangago.me/read-manga/sleeping_dead/ (manga, slightly fucked up but in a good way, mangaka's other works would also fit the bill)

https://www.mangago.me/read-manga/yonin_no_nibiiro/ (manga, fucked up in a weird way, crime drama ig??)

https://www.mangago.me/read-manga/the_perfect_relationship/ (manhwa, psychological, fucked up in an interesting way)

You are a live savior

This one is pretty twisted from what I can remember:
https://www.mangago.me/read-manga/honeycomb_child/
https://www.mangago.me/read-manga/honeycomb_child_dj_honeycomb_child/