The speaker describes a relationship that feels doomed from the start. Calling the couple "the new face of failure," they compare their love to the moon: it only seems bright until something better appears, and then it falls. The sun, the stars and the day all stand for love that is truer and stronger than theirs, while the two of them belong to the night.
The feeling is mostly regret and envy. The most striking moment comes when the speaker says they wish they had never met this person, so they could have been "a part of the day" instead. That suggests a longing for a happier, more open kind of love, or perhaps a different life altogether. The phrase "sinful wishes" hints at guilt, as if even wanting this is wrong. The mood is dark, wistful and quietly bitter, with the speaker measuring their love against others and finding it lacking.