Jack headed into the library, rather tired, but still up for some company, and truth be told, not at all above a bit of fooling around, should the opportunity present itself. What he saw as he paused silently in the doorway made him think at first that someone else had gotten a head start on the same idea. Two pairs of boots were discarded on the rug, and a bright pink hoodie was thrown up over the back of a chair. The scene on the couch was incredibly intimate - it just wasn't that sort of intimacy.
Rose was curled up asleep in the Doctor's arms. There were cooling gel packs on the wicked bruises inflicted by Blon, and the Doctor's leather jacket was wrapped around her, so she wouldn't take a chill.
As Jack watched, Rose stirred and whimpered in her sleep. The Doctor leaned down, murmuring something softly, and pressing his lips to her forehead. Rose quieted at once, shifting onto her side and cuddling against his chest. One small hand curled around the soft material of his jumper, and then she was still. A soft smile played over the Doctor's features as he resettled the cooling packs at the back of Rose's neck, and tugged his jacket up over her shoulders.
The Time Lord from Gallifrey was easily the most powerful being that Jack had ever encountered, but he was astonished by the tenderness with which the Doctor treated Rose. Hands that had fought in the deadliest war in known history touched a shop girl from Earth as if she were made of the most delicate crystal. As if he would crumble and break himself if any harm came to her.
And that was when Jack realized a fundamental truth of the Doctor's existence. As much as he might desire Rose - her company, and just, well, her - the Doctor needed her, with the same intensity as he needed the air in his lungs, or the blood in his veins.
Jack's smile was a bit wistful as he turned and quietly walked away from the library.