"I was going to be with you forever," It was one of the last things she had said to him before he placed his fingers on her temples, pushing his way into her mind and locking himself away from her forever. As he did so though he could see the time lines rearranging and everything that should have been destroyed in that one moment.
He ran with her through along pure white beaches and under moonlit nights. Neither one of them ever wanting more from each other then the company and friendship they received. He watched her laughter as they finally made it to the planet of hats. She filled one section of his wardrobe with hats that neither one of them were ever going to wear. He let her though, complaining good-humoredly just because it made her laugh.
He held her and cried with her as she lost her grandfather of old age. He sat beside her at the funeral looking on as they buried the man he would have been proud to call his father. On nights when Donna missed him more then anything, the two of them would land on his hill and gaze up at the stars together. Then they would laugh as Donna shared stories of him.
It would be almost a year after her mother passed when by some strange circumstances they met up with her long lost Lee. He made an exception to his, "I don't do domestics," and Lee traveled with them. Never giving her the twins they had in their shared dream, but instead giving her years of joy and happiness. He was taken to soon though and left her alone once more. The fight the Doctor had always loved about Donna would be lost for awhile, but she would gain it back over time.
Old age would finally come to Donna and he would offer to take her home to Chiswick to leave out her life. Donna to the end would be stubborn though and refuse. Her life was aboard the TARDIS and she was still going to stay with him forever. Forever though would pass quickly as he sat beside her bed and held her hand as she took her final breath. One last time he would return to Chiswick and bury her in the graveyard next to her grandfather and mother.
Releasing her temples she fainted into his arms and he held her tightly to him. Telling his friend goodbye before he returned her to her ordinary life as a temp. The walls of the TARDIS would still echo with what could have been, but in the end even that would just be a memory.