It's focused on the uke. Before he got with the seme, he had his ex boyfriend. the uke had a crush on his ex and the ex lived across him until the ex asked to live with him in the apartment. Over time, things got toxic between the two. The ex had been in debt, and making the uke pay for his mischiefs. If it helps, the uke has black hair and the ex boyfriend had brown hair (i think) and dyed it green over time when he was starting to do crazy stuff. I dont remember much from the seme but he seems to be a celebrity. I know its korean too, i just dont remember the title
Sounds very much like From Points of Three :)
http://www.mangago.me/read-manga/from_points_of_three/

Pls i want angst