Nothing else is. (22)
The shortness of the line and the reversed stress pattern make this line hit the reader hard. And it should. Because it's really weird. He's so in love that literally nothing else exists.
This bed thy center is, these walls, thy sphere. (30)
FYI, the sun is approximately 93 million miles from the earth. So it probably doesn't literally sit ten feet away from the speaker's bed. Not that we're in to bursting bubbles or anything.