Stars spend their lives giving light to others, sharing their heat with everything nearby, drawing things into orbit around them. They are the centre of a universe, keeping everyone and everything alive, like an all-powerful mother, protecting its children, continuing their existence. But all of this does not come without great personal sacrifice, for stars also spend their days burning up from the inside out, a slow, fiery death and when such a monstrous star does eventually die, it creates a black hole, sucking the life from all of those who trusted it, those who depended on it to keep them existing, destroying everything in its wake.

Then, once it's run its course, it will become a miniscule star again, regenerate into something new and hope that this time it won't get so carried away that it will become a destructive monster, yet again. That maybe, just maybe, this time it will simply burn, hurting only itself in its painful death.

That's how I feel, constantly, as though any moment I'll explode and see everyone I've strived to protect get hurt because of me. They will all die, eventually, yet I have to keep on living, continue destroying kind, strong, brave people, because that's my weakness; I cannot be alone, because if I was, I'd soon realise just how completely on my own I am: The Doctor, the last of the Time Lords, the Oncoming Storm.

Maybe the Daleks had it right, the oncoming storm, destroying everything in its path to get what it wants, a vicious tornado, stealing innocent people from where they belong then losing them along the way.

No, I mustn't think like that, I can't think like that because sometimes there are the people whose lives I change for the better, I don't just kill people, I save them too. Amelia Pond, the little Scottish girl far from home, all alone, I have to have saved her, I gave her hope, something to look to, dreams of something better. But I took all of that away from her, I left her, abandoned her, never came back to get her even though I'd promised I would. False promises and lies, that's what Time Lords are made of. Donna Noble, fantastic Donna Noble, saw so much, did countless amazing things, saved the lives of so many, but even the memory of such events would be enough to destroy her, even one tiny glimpse of my face could, in effect, kill her. Rose Tyler, lovely Rose, I hurt her far beyond anything in this world. We were together for so long, she was only 19, I saved her, many times, but not as much she saved me, from death, from loneliness, from myself. Rose Tyler, the Bad Wolf, I took her life because I wanted someone, because I couldn't stand being alone and there she was, bold and brave and willing to leave everything behind to come with me absolutely anywhere. And now she's trapped on a parallel universe, somewhere she doesn't belong, because she belonged here, in the TARDIS, with me. No, she doesn't, she's happy now, she has her life, she has her Doctor, a Doctor that could give her something I never could; someone she can grow old with. Even if, somehow, I managed to return to her world, she would never recognise me, not with my ever-changing face. Anyway, I could and would never do that to her, to any of them, I couldn't hurt my friends any more than I already have done because I'm far too selfish for any kind of good.

But here I am, doing it again, taking another human for my own. Except she's not any ordinary human being, is she? She's the woman who saved my life and, so she'd thought at the time, the one who took it. The woman who can't meet me in the right order, the way it should be. The woman I watched die, the first time I met her. The daughter of the The Girl Who Waited and The Last Centurion, child of the TARDIS, the baby born to murder the infamous Doctor. The woman I am in love with, like I never deemed myself capable: Melody Pond, the only water in the forest, River Song, The Doctor's Wife.

It's the strangest feeling in the world, sitting in the TARDIS with this woman – unbelievably, my wife – when our timelines are almost entirely in-sync. Almost. There is just once event that she is yet to experience, the very first time I meet her and the very last time she sees me; the day that River Song leaves this world forever. But I save her, I do, even when I barely knew her I knew myself, I knew that I would, one day, care about this person more than any other in existence, and I knew that I would have done all I could to save her. So that's what I did, I saved her. Because no matter how hard I try, there is no way around this fixed event in time, the day we met, the first and last time she saved my life, the first and last time I saved hers.

That's why I had to see her, see my wonderful wife, this one last time, to say goodbye, to save her life for the final time. I've just taken her to Darillium to see the Singing Towers, just like she'd told me we had all of those years ago. Then I gave her my Sonic Screwdriver to her utmost confusion, and just as she prophesised, I cried, hoping she wouldn't notice, but of course, I've always known she'd see me. Even so, I'd ushered her into the TARDIS and she'd followed without a word, apprehension etched across her lovely face. Our eyes meet now and I can see that she knows something is wrong, that, unlike most other times, I know more than her. She walks toward me, reaches out and wraps an arm tightly around my shoulders. Her lips form a small, encouraging smile, trying to help me in any way she can because she knows me better than anyone, she knows not to ask, knows that I will not answer, because I cannot. I am so grateful for the understanding of River Song. She lifts her face to mine and those familiar eyes that I'd know anywhere, the eyes that haven't changed since her birth, despite her regenerations, bore into mine, desperate to reassure me, to make me feel safe, happy. But I don't think I can ever be truly happy again, not now that I know this is the last time I will see my River Song.

"Know this, my Doctor," she whispers softly, careful to keep her tone tender so as not to trigger more hurt to seep into my eyes, "whatever it is, whatever has happened, whatever is going to happen, it can't be your fault, for if it was, if there was anything you could do to change it, you would do whatever it took. You know me better than I know myself, so you must know that I would trust you with my life and I know that you would do anything to protect me, as I would you, no matter the cost, but you and I both know better than most that time cannot be re-written, it does not matter how hard you try, I was never able to change the day that I killed you and you will never be able to change whatever is going to happen now. So know, my Time Lord, that I have always loved you and no matter what, I always will."

Her words, no matter how delicate and soothing she had intended them to be, cause my entire being to swell with a guilt so intense that I am rendered unable to look her in the eye. Instead, I settle for a lock of her beautiful, chestnut hair, hanging over her shoulder with the grace of a swan, and I try to give her the entire world, show her my immeasurable pain with my next five words, "I'm so, very sorry, River," and a combination of her confused, loving, pitying look, doubled with the pain and grief of knowing that this is the last time I shall see my wife are enough to send me over the edge. And I cry again, like a little boy taken away from everything and everyone he loves, alone forevermore now that the most important thing in his life is about to be snatched cruelly from him and there's absolutely nothing he can do.

I bind my arm around her, more tightly than ever before, I cannot let her go, not now, not ever, she is mine and I am hers, it was not supposed to end like this; we weren't meant to end like this. In another world, we could have been together forever, without the burden of meeting each other in the wrong order and so me having watched her die before I'd got to know her and her having murdered me before she'd grown up. The thing is, we could actually have grown old together, in a sense, because we can both regenerate, we can both escape death to be with each other. But now I'll never be grateful again for the Time Lord's greatest weapon, the coward's way out. Right now I don't want to exist any longer; if I cannot be with River Song then I want to leave this mortal coil, to die right here, when the last face I'll ever see is my wife's, before she goes to that dreaded library, walks happily to a place where we can never meet again, and then I'd never have to live without her. Maybe death would bring me the peace and numbness that only true nothingness can bring a person.

Carefully, I peel my eyes open through the tears – it seems I had shut them, so deep in the serious contemplation of my own death as I was – and there she is, staring down at me with such a stern look she reminds of her mother, the stubborn little Scottish girl living too far from her home, refusing to change her mind, despite several psychiatrists, that a time-travelling man fell out of the sky and ate fish fingers and custard in her kitchen in the dead of night. And I know she has read my mind, not because she is telepathic, but because she sees things in me nobody else ever has, I sometimes wonder if I betray some sort of emotion in my face, or my eyes, but I know that it is more than that; it is simply because I am The Doctor and she is Professor River Song.

"Do not even think about it. No. I will never allow it. Not in an eternity, you are not leaving me Doctor, no matter what you cannot leave; no universe would last 10 minutes without your existence. I won't let you. No. Doctor, you can't," her voice breaks on the last word and her big, pleading eyes swim with tears that threaten to spill over.

I have never been able to deny her anything, and I'm not going to start now, especially not when I can see how much such a thing would hurt her, especially not when I remember that she does live on in some way, just without me, so it would be my most selfish act to make her begin her new life feeling guilty, once again, for my death, so I make her a promise, "I will never leave you, River Song, I will always be here, The Doctor in the TARDIS, I'm not going anyway, my love."

She searches my eyes for any sign of a false promise, a loophole, even though she knows she will not find one, she knows I could not lie to her and she is fully aware of how completely she trusts me, so she smiles, wipes away my tears and says, "Good. Well, this is my stop, wouldn't want to be late for work, now, would I? I love you," and then she whispers my name in my ear and I know that I would go to the ends of the universe for this woman, and maybe one day that's what I will have to do to fulfil my last promise to her. To bring my River Song home.