When Jack returns he's a broken man. He tells the Doctor about his crew, his lover and his grandson and he tells the Doctor that he'll never be truly happy again. The Doctor pretends he allows Jack to sleep in his bed but the truth is he needs Jack just as much as Jack needs him.
Every night, Jack has nightmares. The Doctor watches him twitch and cry seeing, once again, blood that never should have been shed.
When the Doctor returns he's damaged. He's lost the woman he loves, he's lost one of the best friends he's ever had, he has lost his whole family. He tells Jack that when you live forever you get used to the death, the loneliness. He tells Jack he's sorry, so sorry, about his condition...but a tiny little human part of him is secretly grateful Jack won't be able to die on him.
When Rose finally returns she is alone. She outlived her children, her mother and father and her husband. They grew old and died. Rose stayed the same.
When she sees the Doctor again she asks him how he could have neglected to test if she had the same genes as Jack. He has no answers for her. She curls up with Jack and the Doctor and cries.
She tells the Doctor how much she loves him and how much she loved him.
When the three of them return together they are broken, damaged and alone. But maybe, just maybe they can make it work again.