Listen, I have a ton of toxic bl manga, give me a one worse then non zero sum.

This one’s really bad, not sure why you would wanna read toxic stuff like this though…
- https://www.mangago.zone/read-manga/have_you_ever_witnessed_violence_on_campus/

I'm not sure too tbh

Idk what non zero is but :
Slammer dogs
Corrosive
Exotic love
Wish You All the Best
The yakuza and the widower

I have read all

Lmao okay it's not toxic much but what about "secret relationship"?

Not too sure but i think these are close
https://www.mangago.zone/read-manga/a_married_man/
https://www.mangago.zone/read-manga/a_married_man/