The brown haired guy IS NOT someone to shit on I'll be real. It's not explained here for some reason but in the novel the reason why he gives Sejin his number is because he was worried that the relationship between Sejin and Seju was inappropriate (yk cause he's still a minor), and Sejin didnt have anyone except Seju to rely on. So he gives him his number as a way to contact another adult if something bad happens to Sejin. It's not that the brown haired guy thinks Seju is that kind of person but, he was just making sure Sejin was safe. It was a very sweet and wholesome!
The brown haired guy IS NOT someone to shit on I'll be real. It's not explained here for some reason but in the novel the reason why he gives Sejin his number is because he was worried that the relationship between Sejin and Seju was inappropriate (yk cause he's still a minor), and Sejin didnt have anyone except Seju to rely on. So he gives him his number as a way to contact another adult if something bad happens to Sejin. It's not that the brown haired guy thinks Seju is that kind of person but, he was just making sure Sejin was safe. It was a very sweet and wholesome!