The speaker looks back on a past love and compares it to the moon. At first the comparison is comforting: you don't have to see the moon every night to trust that it will return, and the speaker felt the same certainty about this person. But that trust turns out to be a trap. Months slip into years, the closeness fades into a "mouldering kiss," and the distance goes stale, as cold as an empty bed.
The mood is quiet and wistful, tinged with regret. The speaker admits to being lonely, unable to explain their feelings until it was too late. What stands out is the ending. Meeting the feeling again later, the speaker finds the pain has become faint and remote. The final line, "just like the Moon," turns the image around: the moon is still there, still visible, but far away. The love has become something the speaker can see without being touched by it.