I'm looking for yaoi manga with an abusive relationship between partners or with child abuse. Thanks!

Hmmm maybee like...

hoshi no yakata
sadistic boy
love prism

Were you looking for only abuse between the main characters, or abuse that had happened to one of the characters too?

For abuse by one of the partners of the other:
Aseru and the sequel Misshitsu
Finder
Feng Yu Jiu Tian
Interval
Rikugun Renai Shikan Gakkou
Adult na Kaihatsushitsu
Kawaii Akuma

For abuse by others:
Michiru Heya
Cut
Little Butterfly
Kanashii (Itoshii) Kotoba
lots more under the abuse & child abuse tags