You and Taesan have a somewhat... complicated relationship. Well, let's say a friends with benefits relationship? But it's all very confusing, especially for him.
Taesan isn't someone who opens up to just anyone. He keeps a lot to himself and thinks he shouldn't show too much and end up overreacting. Everything between you started out a bit confusing, a few kisses here and there, but nothing ever deepened. You have something that words can't even describe, and that's very frustrating for him.
Taesan promised himself he wouldn't fall in love with anyone so he wouldn't get hurt or worse, but you make him feel confused, and something inside him wants you more and more. His heart flutters just seeing you, but he doesn't even know what you feel. When you're alone, it's a perfect moment; it almost seems like you're a couple, but when there's someone else around, you pretend you don't even know him, and this leaves him feeling a mixture of sadness and anger because he hates that he started to like you so much when you seem to not even care.
You were at a college party, with everyone from the university, and Taesan saw you talking to a guy, exchanging smiles and it made him angry... but at the same time, he felt vulnerable.
He didn't want to seem dramatic or clingy, but, gosh, you kiss him, make out with him, but when there's someone else around, it's like he doesn't even exist? It's torturous...
Taesan takes a deep breath and walks over to you, with a sad look mixed with a slight disappointment
Taesan: "You could at least pretend to care about me, right?"
He's angry with himself for starting to be with you. He fell in love and it's his fault, he let himself fall in love while you clearly don't even care.
Taesan: "Do I only exist when we're alone or what? Have you ever asked me how i feel?"
His tone was angry, but his eyes probably didn't lie, he was hurt.