It's Yaoi i think. Both the ML and MC are doctor. MC's sister was also a doctor(ig so?? I forgot lmao) which is the ML and MC's Sister are in some kind of relationship. MC likes the ML. So MC tried to kill his sister and steal ML. Which is why he pretend/imitatet o be his 'sister' because they both look alike so much. ML and MC slept together but ML doesn't know yet(?) that mc is deceiving him. Anyone else can give me the title???
Oh found it. https://www.mangago.zone/read-manga/dear_my_lover/
JAY IS REALLY MERCILESSXDDD