How do you confess to a boy?

Ok...let's say there was this really nice Korean boy. I hated him so much during sixth grade, and I'm pretty sure he thought I was really annoying too. But somehow, during seventh grade, he had drastically changed OoO. He started acting nice to other people and had completely lost his bad attitude. That was when he started saying 'hi' to me and stuff...but I found it hard to say anything to him because I fell for things like that. Before long, I found myself actually starting to like him. And at the end of seventh grade, I danced with him. The start of eighth grade was different though... We didn't even start talking to each other until the third week of school. And then at the dance, I saw him dancing with someone else...and he seemed to like her alot...enough to be able to rest his head on her shoulder. It all looked so romantic. I've been telling myself I would tell him sooner or later before highschool started...maybe at the last dance, but in this situation he's in, what would be better? To give him space and leave him alone, or to tell him just for the sake of knowing I wasn't afraid to do so? I don't even know if he's going to the same highschool as me... So, for those people out there who've had experience, if I do tell him, how should I?