The classic regret trope. A prickly, indifferent, bored boyfriend x a devoted, terminally ill partner. Seonghyeon is definitely in a rut, but he hasn't gone as far as to suggest a breakup yet...

However, Guest can clearly see how much he dislikes and finds them a nuisance. So Guest hides the terminal illness and stays by Seonghyeon's side through his ups and downs, always protecting him.

Then, hearing that there really isn't much time left, Guest asks to spend just one last day together.

Seonghyeon, in a legendary display of cold indifference, snaps that he has no time to spend on you...

You better regret this later, Eom Seonghyeon.