I like this boy but...?

Obviously, I like a boy. I'm 14...and I know it's not serious or anything but the obsession is killing me, it's almost like suffocating. I know this is going to be so agonizing to read, with all the confusion rattling my brain right now I am using punctuation horrifically. I have known him for almost three years now, we have been friends, joked around, etc. But he's always trying to make me laugh when I'm around him...and he's different on his own, he's more caring. I walk home with my friends, and he walks home with his, and we walk the same way but me and him walk a little further than everyone else. If he walked faster than me and is in front by more than a few metres, he won't turn around and walk back. I don't catch up with him because I'm too shy. But if I am in front by more than a few metres, he will run to catch up and walk with me and in those few minutes, for a few days a week for the past 3 years, I have grown to really like being with him...I blush if he dares look at me, I cannot stop smiling, it's like the corners of my mouth are semi-permanently hinged. I talk to him at school too, but there's this really popular, skinny, pretty girl that flirts with him. She gets to sit next to him in lessons a lot, and I can't help but stare at them. I hate it so much. She's changed him from the sweet shy guy he was. We still talk walking home, just not as much. I hate being so obsessed and feeling so controlled by him? He isn't even aware of it, so I don't know why...can anyone help? Shall I just get over him, or is there something there?