nine2006

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/

Honestly I probably read them all like you and what quenched my thirst was "alpha predator" a novel that had like 170 mini chapters

99.99% Lovers ,,, okay maybe not the most satisfying of chasing arcs, but I loved how over the top it went