It would have taken very little at that point to tip the Doctor over into real, urgent arousal. But right then he was finally relaxed and calm, and in control again. He kissed the Master again, light and warm and brief, gazing into his eyes from a distance of about an inch, then pulled away - literally moving back a bit along the sofa, his hands smoothing down the Master's arms and down to his hands and holding them together between them.
He smiled at the Master, calm and sad, and... had no words.