Ruby looked up as he broke the kiss, pulled away from her slightly. He was worried, about what he might become, about becoming some evil thing. But thats not what she wanted for him, not at all. Besides evil was such a subjective term anyway.
"I trust you. And you know what I think" she began, coaxing him back down to her, pulling him back in, with words and actions. "I think you'll be you. Just you...at your full potential, y'know. You're taking what Azazel did and making it count for something good. Killing Lilith. When I talk about all this, thats all it is. I want you strong and I trust you"
This was the hardest lie she'd ever told. But darkside as he saw it wasn't so bad in the long run. He'd understand when Lucifer rose. He'd see, he'd know how wonderful it was, how freeing.
He'd be everything she'd dreamed and more. A King, a leader, and still hers as much as she was his. Maybe she'd be a Queen in Hell. Maybe every son of a bitch demon that had ever called her a whore or mocked her when Azazel had died would suffer at her hand. Or at Sam's because she willed it.
"You're not going to become something you're not Sam. I promise you that"
That wasn't a lie. Because that was inside of him already, she just needed to coax it free.