Because it wasn't even really love.
In the world, there were many different types of art. Portraits, sculptures, abstracts. After he talked to Namine, he still didn't fully understand what she had meant. A landscape painting leaves an open space to rest the eyes, a space of nothing.
One day, it all made sense. He met the boy that would teach him his place in the world, showing him how he could fit in.
Roxas was a landscape painting in himself, and after Axel met him he started to understand.
Without a heart, Roxas couldn't show envy, love, wrath, pride. These things often ruined the best of people, who always threw their chests forward and held their noses up.
Without those aspects, Axel started to truly appreciate Roxas for who he was. There was nothing there to make him stick his chest out, and his nose was always level which allowed for Axel to look into his eyes, to see the rest of him.
People usually look to someones heart first, but the bond they shared was above all these messy, human traits. They didn't feel attached, they just were. It wasn't love, it wasn't hate, it wasn't anything. They rested in the blank canvas together, for a while, until Roxas left.
Namine had taught him to decorate, fill in and make the gap his own, and there was a hole in his heart where he could comfortably fit Roxas. All the words he never got to say, he never needed to. They all fit into the blank portion of the painting, and the rest was worth a thousand words.
Author's Note: Totally got inspired to add another chapter to this. Didn't think I would, but there you have it. Jen, I need to stop sleeping on our conversations, haha. Or do I? Remember kids, don't own a thing. Axel and Roxas should always be paired as FRIENDSHIP. -is shot-