The Guardian question

When I first thought about writing this story, I imagined Angels as perfect. The typical Guardian Angel that many of us are told about are the ones that fight evil, fight for truth, and guard our every step. But the more I thought about it, I realized that they are not perfect. I mean, Lucifer, sinned and was then casted down to the pit. Right? So, is it realistic to write, or even to believe for that matter, that Angels have their own inner demons?