You said he's your closest friend, it could be because of that too... Why, do you like him? :3 Maybe you stare at him because you have to be if you keep catching him and he's catching you xD
My closest guy friend has started to stare at me during class, and so when I notice him staring, I turn and we have a staring contest for a bit. (His eyes are a beautiful blue XD). Any idea why he's starting to stare?