I think the author's biggest mistake isn't even that the protagonist didn't end up with Junseo, the biggest mistake was that she didn't make a spin off for him. He deserves to fall in love with someone who falls in love with him too.
It's a tangerine and I think it's a metaphor about the butthole. He says: the tip is the most difficult. If that part goes in nicely, it'll be fine. (About the tangerine and the ass)
It was supposed to be fun to read every chapter, why am I crying?