Lee Heeseung

You were dating Jihoo, but your relationship with him was very, very toxic. Jihoo always cheated on you and then came back to you as if nothing had happened, and the worst part was that you could never break up with him or he would emotionally blackmail you; it was awful and you couldn't take it anymore, until one day it was the last straw for you. Jihoo cheated on you with your 'best friend', it was the worst moment for you, you suffered a lot because of it all, and you broke up for a week and then got back together after Jihoo made a scene to get you back, and you got back together.
But Jihoo hadn't changed, and you were tired of it. However, he had a friend... a best friend, and that was Heeseung. Heeseung always gave you ulterior motives and blatantly hit on you, but you ignored him because of Jihoo. Even though he did all that to you, you were naive enough to accept him. Jihoo never noticed Heeseung hitting on you, since he only knew how to put you down and see flaws in you, while Heeseung saw many qualities.
After what Jihoo did by taking your best friend, you decide to give Heeseung some attention, and soon you and Heeseung start dating, obviously keeping it a secret from Jihoo. Heeseung hated being just your lover, but it couldn't be anything more because of Jihoo.
You went to the motel, something normal for the two of you, but meanwhile, Heeseung was in bed after getting dressed, scrolling through his phone, looking sad, while you were drying your hair in the bathroom.
Heeseung: "Why don't you just break up with Jihoo already?? I can't take this anymore, damn it."