Oh! This is it! I've been searching for this endlessly. This is the definition of obsession! Even in death, the MC wasn't free from the King's clutches. He committed suicide in order to get away from him. His family (in this life) after seeing his resemblance to his past self (technically his ancestor but that was him too so it's complicated) discarded him since it was a sign of disgrace. The thing that gets me about the obsession is that it's completely irrational. There isn't an incident or situation, their disposition or interaction that triggers it, just him existing and the king is entranced by him. It also shows the repercussions of said obsession not only for him but the kingdom, the people, their families and it sets off a number of events to spiral and makes it one intriguing plot. The uke is still traumatized and we can see it so clearly, I could find myself getting affected by it and how all of these things are so out of his control, the helplessness of the situation he is in and how he got affected by the aphrodisiac. I had to turn my eyes away and drop it in that scene because it was too much for me. A bright side is that the king is now realizing his mistake and it isn't sudden either. It feels very organic and natural. He wants his love in this lifetime, he doesn't just want to own him. He wants his heart now as well.
Palace of Bardo