Wow I'm so glad that I skipped over the side story entirely. I just wasn't really vibing with it and the weird hinting at the brother being a bit too interested in dojun was uh weird.
Reading these comments it seemed I dodged a bullet so I'm happy. This is like my forth time rereading it and I feel so lucky that I didn't invest any time into the side story lol.
Wish we got more of taehan and doyun with their baby though T_T