He didn't notice it at first, glad as he was to have her back with him, but she would always position herself on his right side, and would always hold his right hand. After a month in this new universe and a month of new memories and hugs and hand-holds with Rose Tyler, his impressive Time Lord brain finally cottoned on.
He paid closer attention, and sure enough, her left hand was twined tightly with his right hand 98.89% of the time.
"Rose," he broached carefully one day, not wanting her to feel as though he wanted her to stop. Gods, did he not want her to stop. "I just realized you're always holding my right hand."
Her legs were curled under her, her cheek was pillowed against his shoulder, and her left hand was lightly tracing patterns on his right hand, which was resting against her thigh.
She glanced up from the novel she was reading on her tablet, her eyebrows furrowing in confusion.
The Doctor made a vague gesture to where she was sitting, to where he was sitting, and to their twined hands in her lap.
Rose's eyebrows furrowed further.
"Oh," she said softly, the muscles of her thigh tensing beneath his palm. "Would you prefer me to move?"
She began to shift away from him, but he stopped her by tightening his grip on her thigh.
"No!" he said quickly and fervently. He gave himself a swift mental kick for even bringing it up in the first place. "No, please don't. I was just curious, that's all."
Rose's face flushed red with embarrassment and her eyes dropped to her lap.
"S'silly," she mumbled, swiping her finger back and forth across her tablet, making the page of her e-book flip forward and backward again and again.
The Doctor doubted that, but he waited patiently for her to tell him more.
Rose set her tablet on the coffee table and turned more fully towards him. She picked up his right hand in both of hers, and began playing with his fingers. He suppressed a shudder that threatened to ripple up his spine.
"This was the hand that first took mine," she said softly. "As my first Doctor, your right hand took my left hand, and you led me to safety."
The Doctor's throat felt too swollen for words, and that was good, because apparently Rose wasn't done.
"Then in that dungeon in Cardiff, with Dickens, when all the ghost people were about to get us, I took your right hand and that was when I knew I could never leave you, and that we would take on the universe together," she continued, speaking faster and still not looking at him. "Time and time again, my left hand was always in your right as we ran across the universe and as I fell deeper and deeper in love with you. And neither of us would even be here if your hand hadn't got chopped off. Or if Jack hadn't found it and kept it safe. I just can't stop thinking that there are so many things that had to happen in just the right order at just the right time for us to be here, together, right now."
Rose finally grew silent, her fingers still tracing his. The Doctor was speechless. He knew that this human life of his was such a statistical improbability, yet here they were. Listening to Rose talk about it, though, and hear that awe and appreciation in her voice sent chills up his spine.
"C'mere," he said softly, tugging her into his lap.
Rose awkwardly straddled his thighs, never having sat on his lap before. She made a noise of surprise deep in her throat as he pressed his lips softly to hers. After a moment, Rose deepened it, threading her fingers through his hair and melting closer to him. She pulled back after a moment of chaste snogging. Her lips were red and her eyes were shining as she smiled brightly down at him.
The Doctor couldn't help but kiss her again, pressing his lips once, twice, three times to hers in slow succession. He grinned when he felt Rose shiver above him.
"I love you," he murmured, raising his hand to trace across her face.
Rose gave him a bright, daft grin, which he knew mirrored his own.
"I love you, too," she replied, leaning forward to capture his lips between hers again.
The Doctor responded enthusiastically, mapping out her mouth with his tongue, drawing identical shudders from them both as Rose scrapped her nails across his scalp.
The Doctor thanked all of his lucky stars, along with his handy spare hand, for this wonderful life that he could now share fully and completely with Rose Tyler.