It was an unspoken rule between them, no matter what, their feelings for each other were never to be uttered when the other could hear. They always had trouble with rules in general, they seemed incapable of following them, but this one they were determined to follow, if only to save the remains of their fractured heart. So they waited, held back the words, held them till night (or what passed for night in the TARDIS), when they could pretend that the other was asleep and that any reply they received was merely their imagination.
"I forgive you"
"I want you"
"I need you"
"Don't leave me"
"...I love you"
All their words, hidden in the pretence of sleep and imagination. For they would not openly break this rule and their hearts would be protected by this bending of the rule, for if they didn't love each other they couldn't be betrayed and when the time came, as it always did, when one of them would leave, they would cling to their 'imagination' and their whispers in the dark.
