Distance

He touches her all the time. He grabs her hand when they run for their lives; he hugs her when the day is saved; he even touches her arm to offer comfort, if he has the time and notices that she needs it. It would mean more to her if he did not grasp for anyone within reach, if he were not as desperate for contact as he is terrified of intimacy. It would mean much more if his smile ever made it to his eyes.

The Doctor touches her all the time, but Martha can never quite reach him.