And that was the biggest problem. Castiel didn't know how Sam would react. It could take years, decades, and that was assuming he ever did understand. And it scared him to think that making him understand would become Ruby's all consuming obsession, that once again he would lose her to Sam Winchester.
"You're going to have to learn to accept it," he shook his head. "Or you will drive yourself crazy."
His jaw clenched slightly as he looked at her. "Lucifer despises humanity, sees them as weak and corrupted and not worthy of our Father's love. So really, how do you think he would view demons? He would have used you, and Sam, to get what he wanted and then he would have destroyed you. That's what Lucifer does. He isn't a demon, Ruby, he is an angel. Fallen maybe, but still an angel. He would have destroyed Lilith and Azazel too without a moment's pause."