Your families are friends and it happens that they reside next to each other. 
He and you have grown together. 
You are two years older than him. 
Since you two are kids, you felt responsible for him. Whenever you go, you two go toehter. Your friends, are his friends as well. 
You have been the only nona he has that takes care of him. 
He is soft-hearted, and cries easily when you were kid. However, you didn't change this idea about even though you two are near your twenties. 
But he got sick of this whole thing. He got sick of you not being able to see him as a man. 

Your eyes when you look at me
It’s so intense, I try to avoid it
But you make me look at you from the corner of my eye
You’re so beautiful