"Dat du mien Leefsten büst" is known throughout Germany as a school song and is supposed to represent a typical North German or Friesian folksong. As a school song it has been bowdlerised in that verses 4 and 5 are expurgated. I suppose singing about sex before marriage even in this liberal and enlightened country is somewhat infra dig.
It has a lovely melody and a joy to sing. I have sung indeed many, many, many times. I used to love singing it with Kerstin Knie where we sang two-part with concertina accompaniment. I've also accompanied the Klingende Runde and the Idle Fellows with the penny whistle.