I think it means a lot that Seo-In is bringing up the past now. If you remember from his past, his whole thing is to just bury bad memories so far that they basically just become irrelevant. His reminiscing about their school years is probably an indication that he's going to more honestly pursue 'something' with Yeongwoon, or at least be more open about his wants rather than constantly playing a cat and mouse game with him
I think it means a lot that Seo-In is bringing up the past now. If you remember from his past, his whole thing is to just bury bad memories so far that they basically just become irrelevant. His reminiscing about their school years is probably an indication that he's going to more honestly pursue 'something' with Yeongwoon, or at least be more open about his wants rather than constantly playing a cat and mouse game with him