When the Doctor next sees Jack again, he's crying.
He lets him sob, curled around him, on the moth-eaten sofa placed in the control room. Jack's tears soaking through his clothes and burning on his skin like tiny embers. The TARDIS hums rhythmically, the twisting coral shapes and golden walls glowing in what could be sympathy.
"I'm going to watch them all die." Says Jack, his voice thick with despair, "Tosh and Owen are gone! What if it's Ianto next? Or Gwen? Why can't I just die!?"
The Doctor says nothing but strokes the man's hair letting the fresh surge of tears soak into his shirt. He never wanted this for Jack, never wanted him to have to act as the father, as the leader, so strongly so that his emotions where bottled and kept to fester and boil, to drive him insane. He never wanted Jack to bear the burden of outliving everyone he ever knew, everyone he cared about.
Jack's sobs are shudders and gasps now.
The Doctor winds his arms around the younger man, the man that has to live forever, and presses a dry kiss to his head.
"Go to sleep, Jack." He mutters into his hair, "I'll still be here tomorrow."
He wishes he could do more. After all, what is tomorrow to a man that has forever?