Have you read Sakura Gari yet? Itou-san? They're both amazing in my book, and so very , very f*cked up. Serious favorites of mine.
How about this http://www.mangago.zone/read-manga/feeding_lamb/ ?
try looking over holic's twisted list http://www.mangago.zone/home/mangalist/57857/
or hers http://www.mangago.zone/home/mangalist/52275/
*adults only* yaoi/shounen ai that u should definitely read(serious stuff):
http://www.mangago.zone/read-manga/let_dai/
http://www.mangago.zone/read-manga/sakura_gari/
http://www.mangago.zone/read-manga/shiiku_gakari_rika/
http://www.mangago.zone/read-manga/kokoro_o_korosu_houhou/
http://www.mangago.zone/read-manga/dark_heaven/
http://www.mangago.zone/read-manga/zankoku_na_kami_ga_shihai_suru/
some other reccomendations based on ur description:
http://www.mangago.zone/read-manga/boys_next_door/
http://www.mangago.zone/read-manga/deadlock/
http://www.mangago.zone/read-manga/warehouse/
recommendations*
Great list (of course! ) but it should be mentioned that Shiiku Gakari Rika is incomplete. The author dropped it because even she found it dark and had to work on something lighter.
I feel like I've read everything now, and I'm just checking if I missed anything (psychological tag doesn't update much). Please suggest a few or refer me to a list. Thanks in advance.
Dark elements: serious gritty stuff, serious societal issues, serial killers, dark fantasy, criminals, prison life, dark scifi or apocalyptic/dystopia stuff, dark comedy. Don't care if its sad or fucked up.