Well if he is unsure/unaware, he shouldn’t have dated yumin in the first place. This half assed feeling hurts more than being hated. And he is still being a jerk if he's stirring things up just to be sure of his feelings
He dated the mc because OF GRATITUDE bcs the mc saved his father, and he thinks that hes obligated to like her. He didn't even consider wether what he's feeling is love that time he considered his "feelings" as gratitude, not love when in fact, IT IS LOVE. its hard to explain but yeah
if its was love and he's unsure, he wouldn't have dated the mc. But the thing is, the mc saved his father so he thinks that he owe the mc that's why he dated her as a way of saying he's grateful. I think he felt like that from the start but eventually liked her but js unaware. And there's something suspicious about the phone call the mc overheard, it's possible that it's a misunderstanding( yk that kind of miscommunication where the mc didn't hear the full convo) don't get me wrong, im rooting for the ml
the ex bf seem to have feelings for the mc but js don't know wether what he feels is love or gratitude(?) he doesn't seem to know that he likes the mc