The season is turning; he can feel it under his feet like a tiny vibration that no one else can sense. As the first autumn leaf announces that winter is coming, so too The Doctor can see his fate looming before him.
He's losing her in slow motion.
After dropping Clara off, he feels the loneliness starting to creep; its tentacles wrap around his chest. A deep sadness threatens to pull him under into a melancholic funk that could last for weeks or even years if he drifted long enough.
He pulls a lever on the console sending the TARDIS into the vortex in a vain attempt to delay the inevitable. He could be out here alone for months and still materialise in Clara's flat a week after he left her. She would be bright and sparkling and the cobwebs of his depression would be blown away in an instant. But how long could he keep doing that for?
Like every companion before her, Clara would bloom and die and he would be left alone again.
He thought about her, all giddy with infatuation at that long-haired ninny, Robin Hood. How she smiled at him and laughed at his jokes. The way she held his face and kissed him tenderly goodbye on the cheek.
He couldn't offer her love. The very thought of it seemed inappropriate, perverse even in this new body. Their relationship was platonic, sometimes fatherly and yet he felt a jealousy and possessiveness build inside him at the very thought of her with someone else. Someone else monopolising her time, desiring her, touching her. For all his brilliance, he would still be undone by some young buck promising her an ordinary life.
He gripped the console, his knuckles going white. He was afraid; afraid of being alone and being left with no companion, no life partner or equal. He was afraid of starting over.
The Doctor was not sure how long it was before he started speaking to the darkness but it had certainly been more than weeks. Or was it months? He didn't really sleep but when he did slide towards rest there was a lingering presence in his mind and the sensation of a cold hand around his ankle. He jerked awake and found that he had drifted off while writing on a blackboard mid-sentence.
The TARDIS pulsed away in the background. The sound was comforting like a mother's heartbeat but he could not shake the feeling of being completely alone in the universe and also feeling a presence nearby.
He dropped the chalk and descended the stairs with a lit candelabra.
"Question," he said into the darkness. "Why do we talk out loud when we know we're alone?" He blew out the candle, sending a lazy trail of smoke upward.
It was not good for man to be alone. Not good at all.