The poem is a quiet snapshot of a morning after a night together. The speaker wakes to fogged-up windows, the scent of her hair, her fingers moving across his chest, and her made-up eyes seeming to speak to his while her lips curve into a smile. Everything is small and physical, and each detail is felt rather than explained.
The last line, set apart and indented, is where the feeling lands: "I had caged a magic." The speaker seems amazed, even a little proud, that he has her close. The word "caged" is interesting, though. It can mean treasured and kept safe, but it also hints at possession, or at the fear that something so enchanting might slip away. The poem doesn't settle which. The mood is warm, hazy and intimate, like the steamed-up glass, with a faint edge of wonder and uncertainty underneath. The title, with its past tense, may suggest the moment has already passed, though that is an inference from the wording.