Family. It's something the Doctor tries hard not to think about. Only madness lies that way, grief and loss overshadowing every happy memory.
Yet since meeting Rose the darkness surrounding those thoughts, that word, has lessened. Here in this street, with three pairs of arms entwined around him, accepting him, he dares to dream of family again.
Rose, Mickey, Jackie, their lives may be fleeting but they make him feel almost whole with their simple embrace and the knowledge that he is loved.