Yoojin (Eugene??) starts off rocky, he's very self absorbed in his own wants but he slowly falls for Minwoo and vice versa. They actually get a lot better at communicating (usual stumbling blocks; one lies and the other overhears it) but they resolve it.
Like someone else said, I can't imagine a third person in the mix, given the point we're at in the story (YJ and MW are deeply in love), but things change. Still, it'd break my heart because they are pretty wholesome in how much they don't want to be separated.
Deep