Ruby knew what was going to happen from the start.
The moment that Lilith had fallen to the ground, she had seen Sam Winchester's face. Special child. The boy with the demon blood. Looking so defeated. Betrayed. Hurt. She knew those expressions well. It was the faces that Sam wore so often, so perfectly. She remembered perfectly. The first time she saw those expressions. So vulnerable.
The first time was because Sam didn't know how to save his brother. Then it was because of his brother's sealed fate in hell. Then it was the fact that he was corrupted with demon blood. But this time, this time was different. This time she was the reason for it.
She was laughing. Exclaiming how she was so smart. So perfect. So awesome.
Sam Winchester's expression grew darker.
She had won. Holding victory with both hands. Hands that were stained by blood and trickery. But she was confused. She wasn't feeling happy. Maybe a little proud about out smarting everyone. About being the most loyal to Lucifer. But other than that she felt like an empty shell. There was no joy about the face the special child was giving him.
Before Dean could break the door. Before Lucifer rose, in that little time they had she tried to convince him. Tried to convince Sam to come with her. He would be Satan's favorite. They would be together. No complications.
She knew the answer before she heard it. Maybe it could've happened if there was no brother. No one Sam could cling on to. No family. Or maybe it just wasn't destined. Wrong time wrong place. Now this was hell. Not that stupid torture that Alistair did. This was worse. Being rejected. Abandoned. Left to rot. Feelings could strike much deeper even if you had a corrupted soul.
She was still human in core. A poisoned human soul, but still.
The door breaks open and she knows what's going to happen. Her arms are held behind by the tortured brother and the special child holds the knife. The knife that she gave them. How annoyingly ironic. She felt the blade sink deep in to her chest. Right beneath the heart. Sam's hurt, she can feel it.
This wasn't what she wanted but she had already known. The lighting behind her eyes strikes once, twice. Before she vaporizes completely, she needs Sam to know. To know that this wasn't her plan. She had wanted Lucifer to be freed, yes. She wasn't going to deny that. But she had also wanted Sam.
She feels it right around the corner. Death. But before that, she whispers. It's loud enough for Sam to hear and Dean to not.
"I love you."
With that her soul is gone for the second time. But this time forever.