Guys listen! I went to the first chapter again just to check something, and I think the person we saw was Shinpei. I mainly think this 'cause the back is quite big for being a female, the hair is also short (they didn't have a hairstyle of some sort) and the clothes they wear are for men (I think).
So yeah, my theory is that they did not end up together. Maybe they were close to, but ended up not happening. That is why it says "I was very happy" (also the fireflies, which are like, a representation of Satoko or something).
What do you guys think? Pls let me know!