Why does natsume love mikan?

Natsume loves Mikan for a lot of reasons. To name two -and most obvious- he loves her because 1. she's not like the other girls who drool all over him, like Permy. 2. He loves her for her personality. She's always happy and optimistic, the direct opposite from him. He doesn't want to admit that he loves her because he's afraid that, if they're togther, he'll cause her to become depresses like himself and she wouldn't be happy. Little does he know, though, that she loves him too.