It's a completed BL Manhwa. Seme is younger than uke. Seme's step mom was uke's sister. Uke was asked by his sister to live with her stepson and fast forward Seme developed feelings for uke. Seme calls uke as "uncle" even during intimate moments lol.
Sounds like this ? https://www.mangago.me/read-manga/my_housemate/
It toook sooo long to get the chapters pile up and honestly I see why. There's so much planning and attention to details in this and the story line is chef's kiss!! The dialogues and the art really