Not BL and I havent read the beast must die but have you read the works by Kim Carnby? Their horror manhwas involve a lot of psychological components, I recommend Pig Pen first that one is more on the psychological side and it’s such a trip. Below is the author’s list of works:
https://www.mangago.zone/r/l_search/?name=kim%20carnby
On the BL side though, this one had me on an emotional rollercoaster for most of it 64 chapters total, completed:
https://www.mangago.zone/read-manga/my_hyung_s_lover/
If you haven't read:
https://www.mangago.zone/read-manga/killing_stalking/
Caste Heaven
https://www.mangago.zone/read-manga/when_night_falls/
The pawn's revenge
https://www.mangago.zone/read-manga/watashi_no_otto_wa_reitouko_ni_nemutte_iru/
Blind play
https://www.mangago.zone/read-manga/perfect_family/
Black mirror
The hidden man
Interview with a murderer
Idk if these are similar but they're good!
You guys! Thanks so much! <3
Anyone know of something similar to the beast must die? Or any psychological thriller type stories? Doesn’t have to be BL