This is fascinating. There are British versions of a night-visiting song in which the same thing happens -
"Then slowly, slowy rose she up
And slowly slowly pulled she on
But when she had the door unlocked
She found he had both been and gone"

And this version goes on to warn that she's well out of it, as "true love is timid, so be not bold" - he's already away flirting with other girls. Alternatively, it could be seen as a warning not to dither but to take your chance while you have it ...

If its origins are so early, you'd expect other traditions to have evolved their own versions of a night-visiting song. Do similar songs exist in other cultures/languages, does anyone know?

Marje