The poem is only three lines long, and its joke sits in the gap between its title and its picture. "Courtly love" suggests knights, poetry, and a lady worshipped from afar. What we get instead is a bottle with "a fine lip," and a lady who seems to arrive together with her "good night."
The wordplay does the work. "Lip" belongs to a bottle, but it also calls up a mouth, a kiss. So the speaker's tenderness may be aimed at drink as much as at a person, or the two may blur into one. The lady and her goodnight feel like part of the same evening scene: a last drink, a farewell, the end of the day.
The mood is wry and a little wistful. The speaker sounds fond, but also lonely, as if the grand old idea of devotion has shrunk to a quiet nightcap. I read it as affectionate mockery, with a hint of sadness underneath.