If he really thought about it, he couldn't remember the last time he had truly been happy. Sure he laughed and smiled, but he had never realized how empty those gestures were until she calls him out on it.
She stands next to the Tardis console, eyes trained on him as she waits patiently for an answer to her question. He looks back at her, and quickly averts his eyes when she raises one eyebrow at him. He sticks his hands in his pockets and wonders when his tiny pink and yellow human had gotten so observant. He wonders if perhaps, he had been away from humans for so long that they had evolved into smarter beings. He snorts to himself quietly, he was absolutely sure he hadn't.
But Rose Tyler had never been like the rest of the human race. From the moment she had risked her life to save him from the plastics, he had known she was different. To this day, he has no clue why he had asked her to come with him again after she had turned him down the first time. After the end of the Time War, he had been left with nobody but the Tardis as a companion and no matter how much she meant to him, she wasn't exactly talkative and he got lonely. Somewhere along the seemingly endless lines lines of time, everything had dimmed significantly. It was like the fire that had lit the universe had been snuffed out, leaving a quickly disappearing trail of smoke in its wake.
Then he had met Rose Tyler and it was like all that fire had fled to her. It surrounded her, almost making her resemble an angel;his angel. From the moment he had grabbed her hand and told her to run, everything had shone brighter than it had before. Despite the return of the fire that fueled his travels, he couldn't ever allow himself to actually be happy. No, he was far too old and had seen and cause too much pain to ever be happy.
When he was around Rose Tyler though, he was tempted to take a bulldozer to the carefully constructed walls he had built up around his hearts. The thought almost makes him laugh; 900 years of never letting anyone in and one human girl somehow makes him undo all of that hard work.
She clears her throat, snapping him out of his thoughts. He stops pacing, and in the back of his head he wonders when he started. He looks at her, leaning on the Tardis console like she belonged there. Like she would be there until the end of time. He takes a step towards her then stops. He wants nothing more than have her next to him, than to have her touch him the way she had touched his hearts, but he can't bring himself to move closer to her. Seemingly understanding him, she pushes herself off the Tardis console and closes the space in between them until they are nose to nose with each other. She reaches a hand up and runs it over his short brown hair. There's a mischievous glint in her eyes as she grabs his coat lapels and pulls him closer until their lips are almost touching.
"Doctor." As she speaks, her lips ghost over his. He wraps his arms around her waist and pulls her closer to him. "Doctor?" This time, there's a question behind the word. She wants a clear answer to her question. He swallows and stares into her beautiful eyes. It was all or nothing and he wasn't going to let someone who was so important to him go. Not ever again.
"I am happy, Rose. Whenever i'm with you, i'm happy." And that's all it takes, because her lips are suddenly on his and he can feel the smile behind it. And that's when he knows that Rose Tyler would try her hardest to fix his hearts, no matter what it takes.