Sirius smiled sleepily as his kiss was indulged. It was a more than pleasant distraction from his lingering fear and pain.
His free hand lifted to stroke along an arm, though rather than the soft flesh and gentle curve he'd expected, it met a harder and broader curve. It jarred him in his sleepy lull, and he opened his eyes. It was dark in the room, the only light a pale streak of moonlight across the foot of the bed. Sirius' sight in the dark wasn't terrible, and it seemed to have been strengthened since he had become an animagus.
For a moment he paused, still inches from the other's lips. He could see the shape of them, the slope of cheeks, and as his hand moved from arm to cheek he could feel the faintest layer of stubble forming. Remus,he thought warmly. Though sleep blurred the edge of his thinking, awareness rushed in at him. At once he felt terrible and elated. He was taking advantage here; of Remus' present state, and kind nature. Not everyone would have offered him this comfort, of not sleeping alone. But it was so difficult to move away. So terribly dreadful to consider not stretching this moment as long as he could, for when would he have another chance?
As though this were some spell he was casting and desperate not to break, he kissed him again with gentle hesitation.
It occurred to him to tell it all now, to his sleeping friend who would never remember hearing it. But what if he woke? Sirius knew he could pass this off as sleep-driven action, but an admittance of his true feelings...He simply couldn't stand to hear what would be a gentle and kind, yet ultimately crushing rejection.
The sadness of holding these things secret was far out-weighed by Remus' continued friendship. Even if he did feel like a traitor to that friendship.