Sight
It wasn't love at first sight.
Hell, it wasn't even love at second sight. Or third. Or fourth.
In fact, he was quite wary of her when he first met her. She was all frizzy-haired, and eager, and brilliant, but scary.
It took awhile for him to warm up to her, and it wasn't until the troll incident that he became her friend.
But now as he looked at her for the millionth time, after years of being her best friend, he saw her.
She was still frizzy-haired, and eager, and brilliant. She wasn't as scary now though he wouldn't want to be at the other end of her wand.
He saw her with 20/20 vision made possible by years of understanding, acceptance, friendship, and love.
And things changed.