He would never admit it to anyone, but Jack loves the sensation of losing control, whether he's in battle or in bed. It's the reason he's seen so much action – so many wars, so many lovers – and perhaps, he tells himself as he feels that surge of impulsive energy approaching, he's just a little bit addicted to both.

The Doctor's teeth are working at the sensitive skin where Jack's neck becomes his shoulder, and it's pushing him to the limits of his endurance. He's got to let go, can't hold back any more, but it's too soon, far too soon. This can't end. This fuck he's shed tears of frustration in his longing for. The conflicting desires to crash through the barrier and to hold back, savouring it as long as possible, are going to tear him in half any second now, but he knows he really doesn't have a choice – he isn't the boss on this ship, and the Doctor is calling all the shots. When he senses Jack losing it, he holds back, stops his a-rhythmical thrusting, and treats Jack to a long, lingering kiss. Jack wants to deepen it, quicken it, indulge in it, and get back to the fucking all at once.

But the Doctor knows him too well. Jack has allowed him more glimpses beneath his tough-guy exterior than any other being in the universe, and now the Doctor knows how to play him. Jack can't tell how close the Doctor is, can hardly read him at all, but he's sure now that the Doctor has always wanted this since the moment they met. He's always looked at Jack differently to other humans, allowing for a begrudged iota of respect, and beneath that something else – the knowledge that Jack might actually prove a match for him in a variety of interesting ways. And now he's looking at Jack with that same expression, newly tinged with the hot flush of lust. He quirks a cheeky grin at Jack, then nudges his head to the side. Jack can feel lips and teeth working their way up his jaw line, and at the same time the Doctor moves again, gently, softly, infuriatingly casual.

It's his weak spot. He's never told the Doctor, and he hasn't given away any hints, but somehow the Doctor knows to stop just beneath Jack's earlobe, tongue flickering softly in the curve where that bulb of flesh joins the skull. Jack can hear himself groaning with anticipation and then it comes; the Doctor breathes against his earlobe, never touching it with lips or tongue, but the warmth and the peculiar sensation are enough and far, far more.

The tingling echoes through his body, and Jack knows holding back isn't an option any more. He stops trying, stops thinking, and gives in to feeling. Allows his body to rule over his mind. He shudders, and his back arches, and his shoulder blades dig into the soft sheets. The Doctor's hand is helping him out, the other gripping Jack's hip as they are both suddenly gripped by that most primeval of impulses – the desire to push into each other, to become one being, to never, ever, have be alone again. It's never worked before, but just this once Jack can see the faint possibility that the future will be different, that he and the Doctor will be able to walk freely in each other's hearts and minds in pure understanding and completeness – always.

And then it's over, and immediately Jack feels himself falling away, as if the bed has been pulled out from beneath him. Everything is suddenly starkly real and in focus. His limbs are heavy, his eyelids long to close, but a bolt of fear shudders from his feet to his heart as the Doctor slides off the bed and turns his back. Jack isn't one for excessive cuddling, but his usual rules don't apply to the Doctor. Even now, in the erotic afterglow, he can feel that longing to have the Doctor, to possess him, to be utterly accepted and loved by him, as if being the centre of the Doctor's attention – of his life – is the only goal worth fighting for in a meaningless universe. And he was so close. It hurts more to see the Doctor turn away from him now than it did on the Gamestation, listening to the ship's engines fade away.

He can't move, can't speak. The words 'stay with me' die on his tongue, because he cannot beg for this. The Doctor has to want it as much as he does, or it's worthless. So he lies on his back and listens to his own laboured breathing, and the sound of the shower, and wonders why the Doctor bothers having a bedroom if he doesn't sleep, and doesn't make a habit of getting this close to his companions. As the fear trickles through his blood and spreads throughout his body, he tries to distract himself. There's artwork on the wall, just prints, all of pictures he doesn't recognise, all mundane, all added as an afterthought, to make the room seem lived-in. Or perhaps, he realises, the room didn't exist at all until it was needed, and had begun its life the moment the Doctor finally snapped and shoved Jack against the TARDIS console, cutting off their banter with a deep, spontaneous kiss.

And maybe tomorrow it will be gone again.

He still can't move when the Doctor reappears, fully dressed with his tie straight and his shoes on. There's a moment when their eyes meet, and Jack wills him to remove the jacket and come back to bed. Not a flicker of emotion shows behind the Doctor's eyes.

The door closes behind the retreating figure, and still Jack cannot move. He wonders if the Doctor will kick him out at their next stop, if he regrets this, if he hates him. For a while he thinks his world will end if the Doctor hates him, but he knows, underneath, that the reality is even worse.

For Jack, this was the achievement of a lifetime; for the Doctor, nothing has changed.