Yes Kafka, yes.
Also, I've got this, but I warn you this is mentally draining manga because it has messed up characters and circumstances.
I've been waiting to recommend these for so long because I need others to suffer with me:
*Psycho by K.S. Sihai; it earned its name, mentally draining but horrifically artistic. A scary beautiful. Yaoi. Keep it fiction.
*Future Diary(Mirai Nikki) by Sakae Esuno; famous for the anime, infamous for pink haired yonder girl, psychologically draining and retch worthy. Hetero.
*Killing Stalking by Koogi; infamous on this site for a while so you might have already read it, you'll time for recovery. Bleach and holy water too. Keep it fiction. Yaoi.
*Stalker's Game by Tan; great for psychology majors to sink into, keep it fiction. Morbidly fascinating. Yaoi.
*Ex vs Stalker by 양욱; if you had this option, you should just run. Creepy interesting. Hetero.
*It's Mine by LuckS; a Webtoon you will become obsessed with and beg for coins. Hetero.
*Lost in Translation by Jjolee; another Webtoon worth your heart and tears. No romance focus but has Hetero couples. The softest and most wholesome on this list.
*Last Seven Days by Hitsuji Hitsujima; a melancholically endearing work that becomes more tragic and disgusting as anything they can think of as sodomy becomes their only hope. Yaoi.
*Naka no Hito Genome by Osora; the tamest on the entire list, right below Lost in Translation. Very adorable, gradually disturbing.
I’m looking for really messed up manga, like one of the characters is crazy or something or etc. also preferably yaoi but I don’t care