If you walk at night,
I will be the darkness.

This actually made me wonder if this line connotes a negative feeling. But then, when I thought about it, at night, darkness is everywhere. So when you tell this to your best friend, that if she walks at night, that you will be her darkness, it means, that you will be with her everywhere. There's nothing to be afraid of because you will be with her.

Beautiful words, @amr008. Thank you for sharing.