Thou must not leave me!

Thou must not leave me!
Though 'tis a mournful land
Through which I travel,
I will but guide thee, hand in hand.
To mysteries thou must in art unravel.
When thou a little way art gone,
Ere the grove's steep descent
Darkening can grieve thee,
Thou backward to the sweet stars shalt be sent;
While I plod on
To Acheron.