A speaker looks across a distance and sees a lighthouse, which stands for another person: someone who was once a friend and later a spouse. The light becomes a way of keeping that person close even when they are far away. In the second stanza the light seems to reach out, and the speaker can see a "sun" in the middle of the night, so the love feels warm and steady rather than lost.
The refrain changes as the poem goes on, and that is its quiet turning point. "Once a spouse" becomes "twice a spouse," then "finally / eternal spouse." Judging by these lines, the relationship has been renewed more than once and is now settling into something lasting. The wine in the third stanza adds desire and a little intoxication, and the speaker still longs to "make you mine." The mood is tender, hopeful, and devoted, with a sense of long-awaited peace.