Disclaimer; I own neither Doctor Who nor Supernatural, just the writing
xxx
"You're leaving?"
The Doctor stopped, hand resting on the door of the TARDIS. His eyes closed briefly, shoulders slumping as he exhaled softly.
"You are, aren't you? Is that what you do? You help people, and then you leave?"
It hurt because it was true. It hurt because he didn't want to leave, but he knew he had to. It hurt because he knew it was hurting Dean too.
"I can't stay." He didn't turn to face Dean. He wasn't sure he was strong enough to.
There was silence, and the Doctor could hear Dean shuffle from foot to foot.
"I know." It almost sounded as though Dean wanted to say more. But no- the Doctor pushed that thought to the side, because if Dean said anything he'd break.
The Doctor; the last of the Time Lords, saviour of a thousand races, unable to look a human man in the eye as he said goodbye. It would have been funny, if it wasn't so heartbreaking.
"You're not going to come back." Another thing they both knew, another thing the Doctor was too scared to voice. His eyes closed again, pressing together tighter, hand clenching.
"No."
"Why not?" And that was it, wasn't it? He didn't know why, he just knew, with a dreadful sort of certainty, that he wouldn't meet Dean again.
Behind him, Dean sighed and stepped forward. When the Doctor made no move to stop him, he continued walking forward, stopping just behind the Time Lord.
"I never believed you, you know," Dean muttered, eyes on the TARDIS, "when you told us you were an alien. I thought you were mad."
"I am mad." The bitterness in his tone surprised them both, but the Doctor supposed it was to be expected. He wasn't too fond of himself just then.
"All the best people are." The Doctor laughed softly, finally turning around so he could see Dean.
"It was good, wasn't it?" He hated himself for the uncertainty in his voice, the desperation for Dean to agree. This wasn't him; this was what Dean was doing to him. And he loved every moment of it.
"The very best." Dean's smile made the corners of his eyes wrinkle, and the Doctor had to fight down an urge to run his finger across them.
Dean swallowed, dropping his eyes to their shoes and running a hand through his hair. Then he raised his gaze to the Doctor's again, and his eyes were burning with an intensity the Doctor rarely saw in humans.
"I'll miss you," Dean murmured, resting a hand on the TARDIS by the Doctor's head and leaning forward.
"You'll forget about me. One day, without realising it, I'll be gone." It stung to say it, but he needed to hear it. He needed Dean to know that he knew it, and that he was okay with it – even though he really wasn't.
"Never." Dean shook his head, tears spilling out of the corners of his eyes, trickling slowly over the laughter lines and freckles and smooth skin that the Doctor had studied so intently. "That's not going to happen."
"Ohhh, Dean Winchester," the Doctor smiled, one of his rare beams, and lifted his hands to either side of Dean's face, "you save the world every day and no one ever notices. No one ever says thank you."
"Sound like someone you know?" Dean replied, smiling too, through his tears. The Doctor laughed, shaking his head, thumbs running over the wrinkles by Dean's eyes, like he'd wanted to for weeks now.
"Of all the people in the world, it had to be you, didn't it? It had to be you was standing there when we arrived, you who stopped us and questioned us and decided to tag along." Dean smiled again, resting one hand over the Doctor's.
"Best decision I ever made," he replied softly, leaning in to rest his forehead on the Doctor's.
"Promise to keep yourself alive?" the Doctor asked after a moment, tilting his head up to face Dean. Dean nodded, meeting his gaze.
"I will if you will." The Doctor's face broke out into another smile and he nodded too, squeezing Dean's face one last time before letting his hands drop back down to his sides.
He hesitated for a moment, not wanting to leave but knowing he had to – knowing Amy and Rory would be waiting for him inside the TARDIS, knowing that the longer he left his goodbye, the harder it would be – and that moment was enough time for Dean to duck his head quickly, pressing his lips to the Doctor's in a gentle kiss.
It was brief, a light pressure to his lips, but it stole his breath and flushed his cheeks, and when Dean pulled back they were both smiling even though their eyes were filling with tears again.
"I guess this is goodbye," Dean said, and the Doctor closed his eyes again, one last time.
"I suppose it is."
"Well…" Dean paused, ran his thumb over the Doctor's lower lip, "goodbye, mysterious doctor. Good luck on your travels."
"Goodbye, Dean Winchester. And good luck to you." Dean bit his lip gently, pushed himself back from the police box. The Doctor paused one last time, throwing a final sad smile at Dean, and pulled the TARDIS door open, slipping inside.
The Doctor watched Dean watch the TARDIS disappear on the screen in front of him, wishing – for the first time in a long time – that he was human, normal. Anything to stop the tears pouring down Dean's face.