It's been a hell of a year. It no longer seems important to Jack that the Doctor is a coward: Too much has happened since then. Jack stayed on the Valiant because he thought he could make a difference. And he did. Every time he thought he drew the Master's attention off Francine or some poor sod of a guard or any other wretched soul aboard who wouldn't revivify, he made a difference. But at a certain point, that doesn't keep you sane.
Duty doesn't keep you sane, either. Jack's new personal nightmare is ending up as somebody's science experiment. No, continuing to draw fire when you know nothing will ever end it, not even death . . . that takes love.
The Master had kept Jack chained in the Valiant's conference room at first. His primary value was as a means of causing the Doctor pain, and he knew it. He could keep running his mouth to keep everyone else's morale up, but what did you do for a suddenly aged Time Lord kept like a dog by an ex-friend he would have given anything to help?
Standing in chains with his intestines on the floor, frozen with shock and waiting to bleed out, Jack met the Doctor's eyes and saw a dark look he'd never expected to see in these new orbs that weren't blue. He knew it when he saw it, because it's what's driven him most of his life. It's what sent him from a graveyard satellite to a time and place with no spaceflight, let alone time travel, all in the hope of seeing a half-mad alien and a blond girl with fabulous hips and a heart three times the usual size again. Mixed in with the grief, like sugar in flour, there was love in the Doctor's eyes.
Every time he looked at the Doctor, he saw love. And when the Doctor had his gaze in return, he gave back not only love, but trust. It wasn't the kind of blind trust that Martha, struggling and suffering in another way down on the planet, could place in the Doctor and his plans. Jack trusts the Doctor to be entirely himself: compassion, grief, cowardice, and all.
The day the Master caught that look between them was the day Jack was moved into the bowels of the Valiant.
Destroying the paradox machine was easy: All he had to do was die. Watching the Doctor grieve over the body of the dead madman, that was hard. Not because he didn't understand the Doctor's mourning someone who'd tortured him, all but committed genocide, and altered the timeline . . . but because, somewhere in the back of Jack's mind, he did.
He might be ancient for a human, but for an immortal--or even an exceptionally long-lived alien race--Jack's just a baby. He's just now making the transition from fresh shock and grief each time he loses someone to the constant background hum of grief beneath brief, bright moments of joy. Death is a condition of the universe. Anything that defies it is exceptional.
If he'd had an enemy for the last hundred and seventy-odd years, someone he saw often and felt strongly about, he wouldn't mourn that loss. But he can see how, some day, he might.
We keep struggling to live. We keep mourning death. And above all, we keep living.
Jack can't be what the Doctor needs right now. This year that never was might have washed away the pain of the Doctor's abandonment, but it will take the Doctor time to heal. Time to see anyone as something other than a poor replacement for a Time Lord. Time for his nerves not to twitch each time he hears a bell ring. Time to learn to look at Jack without a subconscious overlay of blood and viscera.
And it will take Jack time to stop hearing the hum of the Valiant's engines in his fractured sleep. Time to learn to laugh again without forcing it, without hysteria edging the sound. Jack's never forgotten how to love, not in a hundred forty years, but it'll take time for him to remember how to act on that.
So he'll help smooth things over for the battered souls aboard the Valiant. He'll help the Doctor repair the TARDIS, because no one else in this century can. And then he'll go home to the Hub.
He'll quit keeping Gwen at arm's length just because he knows he loves her. And he'll quit pretending that the easy sex he has with Ianto is all he wants, and see if there's anything more between then. And someday, when they've gone from him and the Doctor has remembered how to love without the grief, he'll go looking for his Doctor again.