Thanks much to everyone who has left a review! This is the conclusion.
A few hours later they stood together in the door of the TARDIS, wrapped in each other's arms, looking out over the now-restored Thames from a safe distance.
"Did you have something to do with it drying up?" Jack asked suspiciously.
The Doctor only smiled.
"So what's your plan now?" Jack asked.
The Doctor shrugged. "You know me. Wrongs to right, worlds to save. It's what I do."
He turned in Jack's arms to look at him. "You could come with me, you know."
Now it was Jack's turn to smile. "I could."
"But you won't," the Doctor finished.
Jack kissed him. "I want to. You know that. But I have a life here now. It's not much of one, but it's mine. And I want it. Even more than I want this."
The Doctor nodded. "You could stay here," Jack countered with a grin.
"What, and be locked in a cell next to a Weevil? No, thank you," the Doctor answered tartly.
"I'd visit you," Jack teased.
"I bet you would." The Doctor grew serious. "You know what Torchwood is meant to do, Jack. By rights, you should be locking me up. Or something."
"Tempting as it is, I can't do that."
"Not one of the big, bad aliens you need to protect Earth from, am I?"
"Oh, you're big," Jack smirked. "And you're definitely bad. But not for the Earth."
"What about for you?"
Jack looked puzzled. "What do you mean?"
"Would you rather never see me again?" the Doctor asked.
Jack exhaled loudly. "O-K, one of us is crazy and for once it's not me. Of course I want to see you again. Why would you ever ask that?"
"Well, there's Ianto, and Gwen—"
"What about Gwen?" Jack asked quickly.
The Doctor shrugged. "I just get the feeling there's something between you two."
"She's just my friend."
"For now," the Doctor said.
Jack decided to ignore that. "And Ianto… it's not like that. We're healing each other. I care about him, but it's not like…"
"Like I love you."
The Doctor sighed.
"Look, I don't care. I don't care if you don't or can't love me. It doesn't change how I feel."
The Doctor's eyes hardened. "And where do you get off thinking I can't love you?"
Jack swallowed. "Rose…"
"Is gone. Alive, but gone. And yes, I'll always love her. I'll also always love Sarah. And Tegan. And Ace." His gaze softened as he added: "and you."
Jack nodded slowly. "Fair enough. But you disappeared on me once, Doctor. Don't do it again. Not for too long. Or next time I will keep you in a cage."
Jack glanced down. "I've always wanted to shag over the Thames."
The Doctor kissed him. "I think I can oblige, Captain."
"Where could he be!" Gwen exclaimed. "He was here a minute ago!"
"Who was?" a voice asked innocently.
They spun around to see Jack coming through the opposite door. "Jack! Where did you go!" Gwen exclaimed. "One minute you were here, then there was this noise, and this wind… out with it, mister!"
"Oh, nowhere in particular," Jack said airily, patting Gwen's shoulder and kissing Ianto on the cheek. "I just had to have a quick visit with a Doctor."