Well he doesn't know the truth about what happened that night when Seul Hae's dad was killed. He only knew what…
If he doesn't have the guts to confess his love. Then he shouldn't interfere in between others. He is one of those characters who believes that they need to protect the FL. And I think that he is acting cheap. By targetting the ML. Just because he was some judo champion he thinks he can target the ML and single him out during training. Also his attitude was not nice when the ML helped the police to catch the druggies. He believes that the ML himself is a druggie. If he has so much of free time. Why doesn't he looks into his father matters. Who is a corrupt police officer.