Weed? I ship them too, but I don't think it was that. lol I think Seo's door swings both ways though without a doubt, or maybe he's just that manipulative/sadistic to use guys/girls to that extent, but he's too obsessed with Hanmi to give up on her IMHO.
I think he just wants to be accepted at this new school at the end of the day and will try anything to make it happen even using guys for his amusement (if he's doing that which again author is so mysterious with true intentions minus a few exceptions). You kind of see that same thing when he's talking to Gun. That he can also use to say see Hanmi I can be normal. lol SMH
What were Seonghwa and Gyeongtae doing in the bathroom that Seonghwa must get rid the smell off? Were they smoking? What? What were they doing?