How do you tell if a guy likes you?

So I've known this guy since fifth grade and we've always had a pretty big rivalry. We argued over pretty much everything and he usually went out of his way to tease me. Admittedly, I did the same to him, but I was making fun of him because I don't like him. I assumed (and I still do) that he was doing it for the same reasons, but his friends and some classmates I'm less acquainted with insisted that he was in love with me. I don't see him as often anymore, but when I do our interactions are pretty much the same as always.