The Doctor only truly loved one other being in existence. She was the one he thought about most; even when there were others with him, he never forgot her. She was everything. He would never love anyone else, not like this; how could he? Nobody else came close to what she meant to him. Time and again he'd thought he'd lost her; but something kept drawing them back together, some rightness in their relationship that withstood the test of time and the crossing of universes.
The Doctor smiled and ran a hand along the TARDIS's console. His one true love.