I had a childhood friend whose parents were friends of my parents, and she would stay with my family after school until her parents got off work.
We got into a lot of hijinks together and I think we had a mutual crush on one another at that age, but we both didn't realize what it meant. Her dad and my dad were eventually assigned to different military bases, and we all ended up moving away from one another (though my parents and her parents stayed in contact).
We met again for the summer after we both graduated high school. Her family decided to stay with us for a vacation. We ended up reconnecting and had a bit of a summer fling, culminating in the two of us sleeping with one another while trying to hide it from our respective parents.
Unfortunately, that was the last we saw or talked to one another as we both started university. From what I heard from my parents is that she eventually met someone in university, married him, and now they have a child together.
It's not unrequited in the conventional sense, but I did think we got along well enough that I thought we could have stayed together if our circumstances hadn't been so different.