A weird incident

In school, there was a guy who always sat on the last bench.

Didn't talk much. Never caused trouble. Just sat there and drew stuff in the back of his notebook. One day I asked him what he was drawing.

He showed me a sketch of our classroom.

Everyone was there. Me, my friends, the teacher, even the guy who was absent that day. I laughed and asked, Why are you drawing us? He just said, I like remembering things before they change. A few weeks later, he stopped coming to school. Nobody really talked about it. Years passed. Yesterday I found an old notebook while cleaning my room. It was the same sketch.Except I noticed something I'd never seen before.There was one person sitting beside me. I don't recognize her.

And I'm pretty sure that seat was empty.