I'm really sorry to be the bearer of bad news but this is really how it ended ):
I think either
(A) author had a significant budget cut
(B) author had a significant motivation loss
or (C) author was writing this on the moment and it wasn't thoroughly planned.
Honestly if they wanted to make a coming of age for Seungho, they shouldn't have marketed as a BL because neither we got actual romance, nor we got integral character growth. At the end it felt as if all characters were tools in Seungho's growth journey, and it didn't feel fair or cohesive at all.
Also he fucked up two different timelines A LOT. Specially the 2nd one, he traumatized Cheongu #2, it's not like everything would be solved simply leaving.
I love the premise for this story, but the development was terrible.
This is extremely good, definitely worth a read.