My new guess..

Reading between the lines a bit, but I think the adjushi DOES hold some romantic interest for Yeongwoon, but he's holding back and contenting himself with more of a caretaker role. This is based on that earlier chapter where Yeongwoon asked why he never dates and theres a heavy pause. Then this last chapter, where we see the ahjushi clearly holds some affection but feels guilty for his role in what happened to Yeongwoon. He's never made a move since but has been looking out for Yeongwoon's well-being.

So yeah, I'd guess he won't turn out to be a full blown second male lead but present enough to upset Seo-In.