Stan.
He was my best friend. Maybe even more than that. Then he left for a month, without a single word. During that time, he didn't talk to me at all and I became depressed. Also the fact that my mum wanted to get a divorce with my dad didn't help. I was completely alone.
Then Stan came back, acting as if everything was normal. It hurt everytime I seen him. We were still friends of course, but we were never 'super best friends'.
I noticed he had stopped wearing the hat I gave him on his birthday, and he got rid of his shoe lace that matched mine.
Maybe that's what hurt most, maybe he had forgotten about me.