more like these

Red Mansion - they both psychos ;))

After killing you

Can you link it? I cant find it

My fav
https://www.mangago.me/read-manga/interview_with_a_murderer/

After killing you:

Eun-seong and Hyun-woo are mismatched lovers. Eun-seong, who loses her temper when Hyeon-woo suddenly announces their breakup, kills him. She holds the body of Hyeon-woo, whom she killed, and Eun-seong, who fell asleep with regret, wakes up with a sense of discomfort. In her arms was not Hyunwoo's but her own dead body. Eun-seong instinctively realizes that he has come from the world where he killed Hyun-woo to the world where Hyun-woo killed him... “We are destined to be together even if we have to kill each other.”