Responses
https://www.mangago.me/read-manga/hit_on_by_a_kinky_guy/
https://www.mangago.me/read-manga/sneaky_red/
very loosely (and maybe even an inversion of what you're looking for)
https://www.mangago.me/read-manga/mr_100_perfect/

what are some bl manwhas where the ML has red/black flag behavior towards the MC but later changes for the better (e.g. grieve, chasing redemption arc)?
I loved manwhas like: beyond memories, heavy rain, 10 years I loved you the most, it starts with Isaac, Lotus and the Lost, …
Right now, I have nothing to read and would love some recommendations!
(づ ̄ ³ ̄)づ