Aloha Co

http://www.mangago.me/read-manga/melo_holic/

Thanks.. ^~^

http://www.mangago.me/read-manga/trash_d_p/

It's marked Yuri, but there's so much gore and the story is awesome (=・ω・=)

Fufu~ thanks desu!!ヾ(☆▽☆)

Hideout is a good read for horror.
Deadtube is also good, I wasn't into it, but it contains killing, gore and a girl who has a unhealthy crush on a guy.
Lots of stuff made by the mangaka 'Junji Ito' is good, disturbing horror.

For gore and horror try Gantz (shudder ... tried the anime and could not get too far) Shingeki no Kyojin, Tokyo Ghoul

hi there~ i LOVE obsessive love and dark mangas too. its like a dark treat haha

BL Obsessive Love

http://www.mangago.me/read-manga/sakura_gari/ (obsessive-longing love)

http://www.mangago.me/read-manga/killing_stalking/
(psychotic in general, with love stuff also)

(many other BL have light obsessive love to a certain extent but since you said psychotic I'll only recommend these because im guessing you want more dark stuff)
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Obsessive Love Shoujo (all of them shoujo/aimed to girls)

http://www.mangago.me/read-manga/flowers_of_evil/ (warning incest. but very hardcore obsessive love)

http://www.mangago.me/read-manga/aishite_kudasai_sensei/ (obsessive love for sensei)

http://www.mangago.me/read-manga/bokura_no_koi_wa_shi_ni_itaru_yamai_no_you_de/ (obsessive love for girl who used to love his brother)

http://www.mangago.me/read-manga/watashi_no_megane_kun/ (both girl and guy have obsessive love for eachother.. my least favorite out of the list but still a good read for obsessive love)

Wahh!! Fufufu~!! Domo arigatogusaimasu desu!!! ^~^ hehehe.. (Killing stalking is one of the best manga that i've ever read.. •~• again, thanxaaa!!

heh~~~ you're welcome my friend ^__^!!!!