I had one. We started dating when we were pretty young (not that I'm much older now, but I think saying that said that I have matured since then would not be an understatement), because we were both 12. It was... pretty awkward, to say at least, but it's what helped me realize I'm aro. It's kind of a long story, but to sum up - I tried to write a love letter for her, but it didn't come out very romantic, which led me to thinking that maybe it's because I'm not that romantic myself either. So, I did a lot of research, and ended up with the conclusion that I'm somewhere on the aromantic spectrum. I wasn't sure about it, which is why I never exactly specified it to my girlfriend (I did tell her though). We broke up about six months after my realization, and honestly - I felt reliefed. It's not that I didn't like her (back then, I mean, because if I knew what she's been doing when I wasn't around, I probably would've broken up with her earlier), but I felt kind of trapped in our relationship, you know? And don't get me wrong, I'm not saying all romantic relationships are like that, it's just what mine was for me.
P.S. I feel like this explanation is soooo messy... I hope you get what I mean.