In the end, there's nothing he can do to stop himself from loving her. No mathematical formula, no scientific solution, no age-old remedy concocted from the sinews of a foreign land - (except everywhere and nowhere is foreign to the Doctor, and he destroyed the one place that isn't.)
(There was no formula for that either, no E=mc2, and the irony is that in spite of and because of him, it burned).
It's in the little things. The wave of her hair, the glimmer in her eye, the motion of her wiry form crossing a Royal plain, the violet moon spinning overhead. In the beat of her heart when she grabs his hand and he can't quite stop himself from sliding his thumb up to her pulse point, her wrist pale and fragile in his grasp. You might even call it breakable.
(She meets his eyes, then, can feel him, and she doesn't pull away. This is one of those times where he has to remind himself that it still doesn't matter).
It's in her, somewhere lost and godforsaken. That much he's figured out.
Is this what it's like? he wonders. Unrequited love. The kind, perhaps, that she'd once had for him. The kind that hurt (but kind of a good hurt). Back when the stars whirred past her blazing hair in childlike simplicity, like diamonds in the sky ... Back when there was only her, was only him, was only him and her, and a wide open universe at their fingertips. Back when he first gave that to her. Back when he was capable of giving her anything at all. Back when he knew how to do anything but take, take, take, take everything away from her. Was every kind word, every whispered sentiment supposed to sting? Was every smile supposed to sink his heart?
Sometimes he marvels at the sheer impossibility of it all, of the human anatomy, of Amy. From heart to lungs to veins to the blood that sweeps from curve to curve ... everything in perfect balance, perfect harmony, unmatched by any living creature the Doctor's chanced to meet. Sometimes he wonders, when he feels Amy's warm, surging pulse beneath his calloused hand, he wonders why an icy rhythm does not beat back against the bone, cold and unwavering in its thrum. Like his. Like him.
But then he has to remember, he has to remind himself, that he and Amy are not kindred spirits, they are not tandem souls, they do not belong.
He doesn't, at least. Not anywhere.