I don't feel bad for Nano AT ALL. Why should Seo have to come out for her to fucking realize that he's Not Interested?! Hell, he's already explicitly stated that he wasn't trying to get a gf anytime soon, that he just wanted to hang out with male friends, that he no longer even wanted to call her by her first fucking name rather than be misunderstood as dating her.
Shit, she can already tell that he's way more interested in his BFF than in her, like. I'm p sure she'd refuse to understand that he's (possibly) gay at all because it doesn't fit what she wants: a romantic relationship with Seo. Old girl doesn't even want to have FRIENDS. She gets into risky situations so that he worries about her bc negative attention is better than none but like. SHE NEEDS HELP, FUCK.
Culturally, I don't think Seo is supposed to be so explicit as to say "I don't like you like that. I ve never liked you like that. I will never like you like that" but, again, I don't think Nano would fucking listen, like she's outright refusing to learn bc it's not the answer she wants to hear.