So I started reading this story, and because it's so good I am paying for it on Lezhin and all. However: I now realized I prefer the SejuxSumin pair than the blondie girl, Sungji. Should I keep paying or is this headed in the direction of the most profound depression, as it seems to be? lol
Well, since you asked, I'm going to be a nice person and give you a heads-up.
MAJOR SPOILER ALERT, read at your own discretion:
Drop this manhwa as fast as possible if SejuxSumin is your OTP and you can't handle an ending with your ship sinking.
Seju cheats on Sumin/gets drugged and raped (one of the most important points of debate in this manhwa as it is portrayed very vaguely) and they break-up. Sumin doesn't give Seju any chance to explain herself as she is coping with her parents' death at the time and it's is too much for her too handle.
Even after their break-up, they are in an on-and-off sexual relationship for ten years, which does nothing but to help in the process of increasing the toxicity they had from the beginning of their relationship. As revealed in the flashback side story, during the course of their relationship, Seju is overbearing and controlling at times and Sumin is a shy doormat who loses all of her social life in the process of compromising with her. They obviously end on bad terms and have no possibility of getting back together.
TL;DR: SungjixSumin is end game. Seju and Sumin part ways for good (implied). Seju gonna get a new love interest in the next side story.