When I was in elementary school, my former friends and I made life a living hell for one of my classmates. Like to the point of her being in tears 4/5 days of the week. She was a class above us, and we only had class with her every other year, but still.
For the last ten-ish years, I thought she might have committed suicide or something, as I didn't see her at all, let alone hear anything about her.
I just looked her up and she's still alive, but still. The thought that I might have actually been responsible for someone's death has been eating me up for a better part of the last decade.