I don’t think this is it since the bottom isn’t actively seducing the top or even really trying to survive…but maybe?
https://www.mangago.me/read-manga/a_gloomy_delusion/
Cozy Obsession? There's a couple others ill look for if not
https://www.mangago.me/read-manga/cozy_obsession/
Secretary Jin's Confinement Journal
https://www.mangago.me/read-manga/secretary_jin_s_confinement_diary/
Thanks!
It was a bl manhwa about this bottom who got reincarnated into a mafia story and in the original book, the mafia top kills him, so he’s trying to seduce him and act like his lover to stay alive but he actually falls in love with him. It’s kinda a basic trope but anything helps