The best of friends must part

This is on the same theme as All good things come to an end. The words can be found in the chorus of There is a Tavern in the Town:

Fare thee well, for I mast leave tee,
Do not let this parting grieve thee,
And remember that the best of friends must part.
Adieu, kind friends, adieu, adieu, adieu, adieu,
I can no longer stay with you;
I’ll hang my harp on the weeping willow tree,
and may the world go well with thee.

In passing, the hang one’s harp on a willow tree is a to put an end to song and mirth. The source is Psalms, cxxxvii, 2.