They all leave their mark on him. In nine-hundred-something years, it’s impossible for people, humans, aliens and beings to not leave an impression. It’s just that some are deeper than others.
When he finds someone new to travel with, it’s not about replacing the one who’s gone. It's about fighting the loneliness, about trying to ignore the fact that he doesn’t belong anywhere (yet everywhere at once). That he is the last one, the only one. It is about finding adventure and saving lives and putting things right where they are wrong (he doesn’t consider himself a hero, per say, but protecting the innocent in the face of otherwordly evil, he has to admit, is pretty heroic).
It’s not about his companions – it’s not even really about him, in the end. It’s about the world – every world – and all their universes. It’s about touching those worlds – seeing, experiencing, changing, saving, living.
And who wants to do all that alone?
He misses her - desperately. He doesn’t compare how he feels this time to any other time he’s lost a companion, because they’re all separate and unique and he feels for them in entirely different ways. Besides, for the most part, it doesn’t do well to dwell on the past, and he has a lot of past to dwell on. No, just here - just now. He misses her, desperately.
And there are moments when he forgets. Moments when Martha says something, or the way she reacts or stares in wonder at the world he’s showing her, and for just a small moment, he forgets that she’s not Rose. Things feel normal – which is a word that, really, shouldn’t apply to a time-traveling police box containing one time lord and a companion of his choice, discovering (or re-discovering) any and every time and place. His hearts swell just a little as they gaze at the amazing things before them and he almost says something he would say to her, to Rose – perhaps her name, an inside joke, a crack about Mickey (Rickey?) – but then the moment is gone, and Martha is Martha. Not Rose.
He tries to hide the disappointment and sadness, because Martha is lovely and mad fun to be around, and she’s trying. She’s always trying so hard to fill the empty place she doesn’t understand, she wants so badly to be closer to him, to be here, and be what he never had the chance to have with Rose. He can see it when she looks at him sometimes. But instead of making him happy, it makes him hurt all the more – because lovingly? That’s the way Rose used to look at him.
It’s not her fault – not Rose’s that she is gone, not Martha’s that she is not the spunky blonde who stole his dual hearts. Had him falling in love before he realized it, before he ever had the chance to say it, to properly kiss her (when one of them wasn’t body-snatched or exploding with the time vortex). When one of them wasn’t a mere hologram on a beach in Norway, running out of – ironically, he supposes – time.
I’m burning up a sun just to say goodbye.
When Martha leaves, he feels the loss of her sharply. Not in the same way as Rose (no, never like Rose), but it stings nonetheless. As soon as the door shuts, that dark, consuming cloud of loneliness rushes in to fill the space in her wake. Deep and thick and wrapping around him like chains, clogging his throat like smoke.
He does wish it hadn’t become complicated between him and Martha. He never intended to fall for anyone (that’s one of the rules, isn’t it? Don't fall in love?), but he had for Rose, and there was no room for him to fall for anyone else – not yet, maybe not ever. He’s sorry Martha fancied him when he couldn’t fancy her back. He’s sorry they couldn’t just be friends, be mates, travelling the ‘verse this way and that, and he wouldn’t have to be alone (that word echoes and tastes of bitterness and loss, and he swears it puts new splinters in his hearts every time he thinks it – graduates to a wooden stake when alone becomes reality).
He’s sorry to see her go, even if he fully understands why.
“She wouldn’t want you to be sad,” Jack says softly.
“Do you think that helps?” the Doctor snaps, unable to stop himself. Silently, he adds, Is that supposed to make it quit hurting? Stop the emptiness? Close the gaping hole she left behind?
“Doctor... she didn’t die.”
“She might as well have.” He’s more bitter than he should be and they both know it. After all, the Doctor thinks, It was my fault. All my fault.
They’re quiet for a long moment and Jack takes another deep sip from the bottle in his hand. He sighs and leans back on his elbows. He cared for Rose too, though less deeply than the Doctor, of course. Jack didn’t know her as well as he did. It makes him hurt too though, thinking that he’ll never lay eyes on that smile of hers again, or finish that dance to their song. She was brilliant, dynamic and one of a kind.
“Some days...” the Doctor begins. He seems to decide not to finish his sentence, but a few moments later when it’s like he’s forgotten Jack is there and he’s just talking to the stars above them, he continues, quiet and sad. “It’s crippling. It’s the only thing I can think about. And all I want to do is... disappear. Lay down and sleep for years. Wake up when it won’t hurt so bad. When I’m not reminded of her every other moment, when I’m not avoiding certain moments in time because it was when I met her or when we did this or saw that." A beat, then even softer, "When it’s her birthday and I can face it and keep breathing."
He buries his face in his hands.
Jack can’t begin to understand. He’s not a Time Lord, 900-something years old, having loved and lost a dozen times. He’s loved and lost too, but he can’t think of what to say – what do you say in moments like these? He considers asking the Doctor why they can’t just go back and save her this time. But he knows better: sometimes time can be rewritten, but you can’t mess with your own time stream. The possibility of screwing up your own future is too great – butterfly wings and ripples and all that.
So Jack takes another sip from the bottle and doesn’t say a word.
It’s like he’s unravelling – coming apart at the seams – when he finds Donna. Or, more properly reunites with her when they both happen to be investigating the same alien mystery. He can’t say at this point he believes in “fate” anymore, but this is maybe something like it. First her showing up on the TARDIS in a wedding dress so many months (years? It’s really difficult to know) ago, and now this.
In all his years of travelling, he’s never met someone who wasn’t important, and it doesn’t take long for Donna to graduate to very important. And the thing about Donna is that she heals him. He didn’t even notice it was happening. One day when they’re on an adventure together and she’s making him laugh, calling him Spaceman, he realizes he’s much less broken, less cynical and bitter. That Donna the red-headed firecracker has become his best friend and rock.
She’s not Rose (no one ever will be) and there’s still a dull ache that presses deep in his chest when he thinks about her, misses her. That, he’s sure, will never go away. But it’s not so acute anymore, not so… present. Donna reminds him how to truly have fun, holds his hand tight and pulls him from the edge when he has a dark day, and makes him forget his pain without even trying.
He can never express how deeply it cuts to have to make her forget. To lose her – to fail her too.
And so this is where he stands: one lost to a parallel universe, one who left with a broken heart, one who will never remember he existed. He’s supposed to help and fix and save people. Instead, he thinks, he wrecks things. They shouldn’t call him the Doctor, they should call him the Destroyer.
He’s seen and experienced so much – some days he thinks that’s a good thing. It must be, right? To have lived for so long and made such an impact? Yet more and more, he can only dwell on his failures, on the battles he lost, and companions who can never be the same, never come home. All because he dropped into their lives and couldn’t stand being alone.
The life force is leaking out, the regeneration has started. Normally there’s no question, no thought process: he simply gives over, he lets go, and transforms. This time, however, he’s afraid. He fears what he has become – worries that he has no Rose to make him see the good, no Martha to support him, no Donna to make him laugh. And he can’t bear the thought of dropping into someone else’s life, of hurting another unsuspecting soul (because travel long enough with the Destroyer, he thinks, and there won’t be a happy ending).
He can’t hold on forever, however. So he decides that he’ll remind himself of the good in these last few hours. See the faces of those very important people and say goodbye (however he can without screwing up time streams). Capture a last image of them in his duals hearts and let go, give in, change…
He saves Rose for last.
“2005? Tell you what. I bet you’re going to have a really great year.”