So i don’t think I ever full-on read this coz it’s yaoi, but it was hugely popular here at one point and I remember kinda just following up with it every now and again because it was so fucked and tragic. I don’t think it’s "relationship" quite in the sense you were looking for, but it fits the bill of the description you gave. You’re rooting for him to get away the entire time.
https://www.mangago.zone/read-manga/kokoro_o_korosu_houhou/
And if you’re okay with toxic family: Chi no Wadachi
Honestly, any of the Harada's works fits in this category amazingly. Be warned though, they're very messed up and heavily psychological. I can assure no happy endings and lots of suffering.
For example: https://www.mangago.zone/read-manga/color_recipe/
Also another messed up from another mangaka:
https://www.mangago.zone/read-manga/hogu_hagyeongsu/
I'm sorry in advance for any psychological damage (=・ω・=)
idk if its rlly toxic but once, it was love
I’m not into BL, but I might read them if I’m desperate for the psychological torture
hwangyong's misery
non zero sum
doronuma
river in me
trial
kegare no nai hito
I want to find psychological manga about a person being trapped in a toxic/abusive relationship