There was this girl who grew up across the street from me. We were the same age, so we were generally in the same classes, would sometimes walk to or from school more or less together, etc., both played violin in class, etc. Sometimes she'd be friendly -- I remember one time she rode bikes and parked in someone's driveway and chatted with me -- sometimes she'd act as though I wasn't there; sometimes she'd act mean -- I once stayed inside during recess to make joke "strike" signs for my classmates because a joke was made during class that the kids would go on strike and everyone laughed; when the other kids came in and found them on their desks, I imagined they'd be happy and laugh and be my friends. Instead, they looked confused or mildly annoyed about it -- not one person laughed -- and she tore hers into pieces and threw them in my face. Naturally, she was the closest to a friend I had throughout my childhood.
When my parents separated in the summer after my 5th grade, I went with my mom and moved to a new city. The next I heard of the girl across the street, I was in high school and it was a rumor someone spread mentioning her name. I tried to find her, and couldn't. Then, after high school, I started using Facebook on the idea that people from my high school would suddenly want to be my friend now that school was over.
One day, it occurred to me to look for her. I figured it wouldn't be hard -- I still remembered all of our childhood conversations, so I knew her full name, birthday, and so on, plus she had a very distinctive birthmark that covered about a quarter of her face, so she'd be easy to identify even though I hadn't seen her in years.
I ultimately never found her, and haven't tried in years. I'll probably never see her again. At this point, I don't mind. Sometimes, you just lose people, and you can't get them back. That's not something to lament.
There's also a second story involving someone I'll probably never hear from again, but that one is more personal.