Yeah, I know what you want. You want a love story based on characters with DSM (or compatible) certifiability for the personality disorder of psychopathy, not a romance.
Psychotic and psychopathy are not the same thing. Are you looking for someone who confuses hallucinations with reality, or somebody who is a psychopath?
Something like that?
http://www.mangago.zone/read-manga/hanazono_no_kioku/
well, this seme is basically crazy like while donning a sane mask publicly http://www.mangago.zone/read-manga/sasayaku_no_wa_sono_yubi/
"legit creepy vibe"
http://www.mangago.zone/read-manga/boys_next_door/
Tadayoedo Shizumazu, Saredo Naki mo Sezu. sequel is Don't stay Gold and then Saezuru Tori wa Habatakanai. Maybe what you are looking for. Mangaka is Yoneda Kou.
Itou-san
Psychotic love? An actual, serious one. (doesn't have to be officially declared as a psychopath, but not the "TEEEHEEE I'M SO OBSSESSED WITH YOU LET ME RAPE YOU" (although there are actual psychotic manga like that but. Something with legit creepy vibe)).
Don't confuse it with ordinary twisted love. Specifically psychotic love! Am I making any sense?