Disclaimer: Doctor Who belongs to the BBC and is under the guidance and support of Moffat. Let it be said that if fanfiction writers owned Doctor Who, the seasons would be way better and the character development actually believable.
His body is a raging, blazing inferno, the fire building up from the inside and eating its way out. He's trying to hold on for her, to explain what is happening so she doesn't worry. Her eyes, large and terrified, are all he sees. He wants to reach out, but resists. Instead, he opens his mouth to speak, to tell her everything would be fine, but instead the inferno breaks; his arms fling out, his head falls back, and his cry of pain is lost as the fire escapes and rages out of control.
He retreats into his mind, tears falling, her name on his lips. He's dying, and she's scared, and soon another man will be the one to hold her, laugh with her, and show her things she never dreamed about.
'Please', he thinks. 'Please make her happy.'
He's surrounded in darkness, shifting, formless figures on his periphery, but a light forms in front of him. It soon shapes into a figure, and that figure soon gets hair and eyes and hands and feet. He watches as the form of his new self materializes, looks around, and spots him. "Oh, hello," he says, smiling. "You're the past model, eh?"
He looks at the new guy, a trace of disgust in his eyes. He's so... pretty. Younger, definitely, which is good for her, but... did he really need the freckles?
"I'm glad we could talk," the new guy says cheerfully. "Kinda glad to resolve final feelings, pass on unfinished business, that sort of thing... no one better to hash out feuds with than yourself. No one else gets caught in the crossfire." He clears his throat. "I hope it won't get too violent. Don't want to damage this body before I even test drive it, eh?"
This particular regeneration likes to talk. He thrusts his hands into his pockets, staring intently at the pretty boy. "You. Take care of her. She's all we have left now, you know. I don't want to die for nothing."
His new self sobers. "Yeah. I'm... well, it was worth it. Grateful isn't the right word, for you can't be grateful for yourself, not really, but... she's ours, you know. The best. I'm glad we met her. She makes the silence bearable." He runs a hand through his hair, causing it to muss.
Taking a step closer he adds, "Look, I know we're not comfortable with sharing our feelings, even more so since the war. But I'll do whatever it takes to show her what she means to us."
Looking at this new man, he feels a pang of jealousy, but also comfort. Here was a man who Rose could be proud to be seen with, who could make her laugh, and who could hold her hand perfectly. He sighs and repeats this, the new one's grin widening.
"Yes," he replies, sounding proud. "Yes, she can. And will. You better believe me... well, us... when I say that."
"Protect her, or by Gallifrey I'll find a way to murder you with my bare hands."
"Suicide?" The pretty guy protests."Seriously? That's new. Haven't had that particular death before."
"Shut it, pretty boy. Just swear to me that you'll protect her. I can't... we can't... we love her," He croaks as the world begins to fade.
His new self smiles sadly, brown eyes shining with awe and sadness. "Yeah. We do, that." He reaches out to grab his hands. "Come on, you daft old thing. If you can't trust yourself, who can you trust?"
"Her." That's a given, and he doesn't hesitate. The blackness is closing in quickly, and he struggles to remain for a bit longer.
The last thing he sees with these eyes is the gentle smile and expression of pure love. "Of course. She's our world, now. We won't let her share the fate of Gallifrey."
Content, he lets the blackness consume him, and then opens his new eyes. And he sees her, wide-eyed and scared, and attempts a smile.
Years later, he's burning again, except this time there's no one to wake up to. The long-ago conversation with his ninth self, forgotten upon waking, is remembered; he breathes a silent prayer of forgiveness, even though he still is protecting her, in a way. Doesn't make the pain hurt less, though.
He's surrounded in black, and is soon facing his new self once more. He doesn't waste time, because he's tired, so tired, and simply wants to sleep.
"Don't forget her," he says as he faces his new self. "Whatever you do, don't forget her."
His new self, the one with green eyes and floppy hair, smiles a secret smile. "Never."
For the first time since he left her, he is content. He embraces the darkness, opens his eyes, and remembers. Always remembers, always cherishes. Ten years, a hundred years, a thousand; no matter who he becomes, what he does, who he meets, her name, face, and love survives in his hearts.
His Rose.
He never will forget her.