he talks about her a lot but everytime he mentions her, shes always too busy and hes always lonely. something seem off...or the author doesn't feel like drawing her into the story so she just includes the fact that the gf exists without having to draw her lol
Or he just likes hanging out with Donggyun, but doesn't want to make Donggyun feel troubled or guilty about it, so he just says he's girlfriend is busy anyway
he talks about her a lot but everytime he mentions her, shes always too busy and hes always lonely. something seem off...or the author doesn't feel like drawing her into the story so she just includes the fact that the gf exists without having to draw her lol