Nighttime is always hardest for Obi-Wan, because it is when things are the quietest, and his mind goes down paths he can distract himself from during the day. He's become something of an insomniac, not because he enjoys it, but because at least he can somewhat marshal his thoughts, whereas in dreams he loses so much of his control.

Laying beside Padmé, he 'listens' through the Force, to ensure her sleep stays pleasant. Now even more than earlier, he can feel just how tired she is, in both mind and body. When she turns toward him, he wraps an arm around her, comforting and taking comfort.

In this way, Obi-Wan passes the night, drifting in and out of sleep just enough to keep his body functional, but never enough that he might dream.