Hullo,
I won't go on too much, but this is set at the end of Journey's End (Episode 13, Series 4) so don't read on if you haven't watched that episode yet. I know this plot has been done many times before but this is my take on it and I hope it makes for enjoyable reading :).

There they stood.

Alone and confused, two broken souls on a beach in Norway, the bitter emotions and horrible memories mingling with the salty air and the breath of the three people, standing in the soggy land. What were they meant to do?
Pick up the pieces and be thankful?
Start a new life together when it was all too clear that nothing would ever be the same again?
It sounded and felt so wrong, but they all held onto hope, by the skin of their fingernails. Only time would tell if the doctor had meant what he'd said.

She

looked towards a spot on the beach, where the TARDIS, everything she had dreamt of and worked so hard to achieve, was slipping through her fingers, like sand.
He didn't even say goodbye
She was so close and she cursed herself for letting him slip away once more. He had left her, left her back here, where he assumed she belonged. She was furious with him and with the world, how could he decide where she belonged, she was twenty five surely it was her choice. Tears pricked at her eyes but she refused to cry, she was stronger than that now. She almost laughed to think that before all this she thought the ground beneath her feet was solid, that she could pop into the TARIDS, if she was quick enough she could jump, just make it as he pulled her into his arms and the familiar warmth and comfort of that great ship.

No. This was her life now.

He.

He would have broken down the walls of time and made whole constellations walk the streets of London, astonishing the naked eye, just to see her radiant smile one last time. He shook his head, he knew as well as anyone on that beach, there was only one man who could ever make her happy and it certainly wasn't him.
He closed his eyes for a mere second, remembering nothing but the passion and warmth of that kiss, the first and only true happiness he had ever experienced in his short and brief existence. When he opened his eyes his hand was reaching out to her. He needed her and he prayed, as he took her hand in his, that she needed him too. In that one second he offered her everything,
His hand,
His heart,
His soul.
She held his hand, no longer aware of anything but the gap in the beach, where the TARDIS had stood. She looked into her eyes, a dreamlike haze clouding over her and behind her almost beautiful and captivating gaze he saw the pain, the pain he longed more than anything else to take away, almost brining a tear to his eyes.

Why am I not in the TARDIS? She asked him, without saying a word,
Why am I here with you and not with the Doctor?
Did he ever love me? He never said.
Was I just lead on like a stupid little girl?

The questions span around Rose's head until her head was pounding, nothing was simple anymore, nothing was comfortable and nothing was easy anymore. Even the sight of someone, identical in every way but one, to a man she loved and adored burned her eyes. She turned and walked away, almost running towards her mother, in fear of the man on the beach.

He stood at the end of the beach, watching her run away and although he would never admit it, watching her walk away was the scariest thing he would ever be forced to endure. It was an image that would haunt him for many nights to come. He held onto hope, since it was all he really had left as the rain began to pour. The memories of his days after the time war came flooding over him and a sense of defeat overwhelmed him as he looked across the beach towards Rose and Jackie, who was waiting for him across the soggy sea.
How did he stand a chance against the doctor, the sainted physician, the mighty warrior, nothing less than a modest superhero ?
He walked towards Jackie, appearing calm and collected, but screaming in agony somewhere deep in his soul.
"She just needs time" Jackie reassured him as they walked up the beach together "Stick with her, she'll come to you in the end"
He smiled and wearily agreed, out of politeness, but he knew, looking at Rose that she would never change.
She deserves better than second best.

Hope You Enjoy.