Why won’t you acknowledge me?

Both Ji-Su's earlier words, as well as Su-Jin's response to them caused Ji-Won's lips to twitch in irritation.

When he finally saw her leave, Ji-Won let out a small sigh of relief. He didn't understand exactly why he was feeling like this, but the fact of the matter was that, the moment he saw Su-Jin getting close to Ji-Su, he felt an uncomfortable sensation inside his stomach. In a sudden burst of hot rage, his body reacted instinctively and he pulled her away from the other man. 

Maybe that was because he knew her situation, or perhaps it was because he simply hated Ji-Su with all his might. Either way, he disliked seeing her so close to Ji-Su.

The latter, though, was unsuspectingly staring at him with wide eyes.

While Ji-Won was having mixed feelings about his interference, Ji-Su was eyeing his brother attentively. Even through the night that surrounded them, he could still see the bubbling fury that flashed inside Ji-Won's dark eyes.