They’re all gone. Rose, Jack, Martha, the incomparable Donna Noble… Each and every one of them left behind. Lady Christina would have gone with him willingly. They could have been great together, he could have shown her so much, the whole universe and all of time, but how could he do that to someone else?
He broke them all eventually. They joined him full of life and eager for adventure, but in the end, for one reason or another, he lost them all. He couldn’t bear losing another one. It would be better for everyone if he travelled by himself.