Everyone here wonders if the ML knows he likes her. I'm about positive that, not only does he know, he's known for a while. She just acts so timidly around him that he thinks she doesn't like *him*. This is basically one of those dramas where 5 minutes of complete honesty would fix absolutely...
The headpat was weird, but I think it just illustrates how socially awkward the sunbai is. Kinda feel for the guy. Not shipping him, but I hope he finds an equally awkward girl to bump teeth with.
@icarushector I'm pretty sure they are all related. Doesn't mean one of them can't feel something ... inappropriate towards a sibling. This ain't the kind of comic where it will likely go anywhere, but it is still an interesting story point.