well i'm looking for some yaoi that has a crazy or mentally unstable uke or seme, any suggestions?

These might not be exactly what you're looking for, but one or the other, or both, are plenty unstable in these.

Sono Kuchibiru ni Yoru no Tsuyu
Tenshi no Uta (NISHIDA Higashi)
I'd call the seme in Aseru and the sequel Misshitsu a bit insane. But that might just be me.

Akutai wa Toiki to Mazariau and sequels

Koi Shika Dekinaiyo - former student basically is stalking his teacher, but it's kind of played for laughs

Bronze and its sequel. Seme is obsessed with uke.
Fukuin Uke is an insane masochist.
Zankoku na Kami ga Shihaisuru All the characters are pretty screwed up in the head there.
Totally Captivated I guess? Seme seems pretty crazy towards uke.

Sasayaku no wa Sono Yubi seme is a Sadist
Mujihi na Otoko the uke has insecurity about himself throughout the series.
Mujihi na Anata (sequel)

lιvιɴɢ ιɴ α yαoι woɴderlαɴd
-QaF-

new york new york

Negai Kanae Tamae, the uke is kinda mentally unstable. ♥

I remember a story in which the uke has mental illness and he is manipulated by an older man (who was his private teacher). The uke has also a twin who "loves" him and want him back. In the end both of them has sex with him. Unfortunately I don't remember the title sorry...I tried to find it, but I don't know how to do a research with more than one category >__<

Found it!! Nureru Karada (YAMAKAMI Riyu)

Dunno if you were looking for darker stories as well, but Sakura Gari has many unbalanced (insane... >_< ) people, including the seme...