
I feel you. Altho I do like the side couple too, its absolutely annoying to see the author abandon the main couple. Especially someone like me who has read this manhwa after long breaks (since it updates kinda slowly) one time I even forgot the plot of the main couple!! I had to literally force my brain to remember their story.

I don't know how many times this needs to be said but: there is no "main" and "side" couple. All four characters are the protagonists and they're equally important. It's fine if you prefer one couple to the other but the author's intention is that they're both mains, which is why the story is written the way it is
SPOILERS
So yet another misunderstanding from lack of real communication is happening with these 2. San thinks that Eunjae is using him as a replacement for his "ex" and thinks Sunjae doesnt really like him. The thing I hate about this story is whenever it gets to something really important with San and Eunjae and want to see more the author switches to the other characters I don't give a shit about for like a dozen chapters, and here it's happening again