He looks jealous. It's gonna be a one-sided love from the secretary to Mr. Joo, and he's gonna be doing things to separate Yeonmin from Mr. Joo, like the scholarship...fully funded education, no need to be with or around Mr. Joo or work all those jobs.
Training = Internships when on break, more than likely paid...
That's why he's suspicious!
Oh I thought he looked uneasy cause the top is doing all kinds of things without telling the MC.
I think I agree this one must be the cause. He doesn't have any love interest to Yeonmin. He just worried all the things that daddy did will bite him one day.
Am i missing sum? Why the secretary looks sus