It's one of those half remembered songs, it might have come via John Renbourn, it might be mediaeval, it might be something else entirely. I've got the tune, and some of the words, if anyone recognises it and can point me in the right direction to find the rest, or can fill in the gaps, that would be much appreciated.

My sweet and fair lady
Never believe of me
That I have bent my knee
To anyone but you.

(less sure about this bit...)
And with no thought of cheating
(and then a big gap)

(It ends with something like....)
Alas out of charity/sympathy
Grant some relief to me
Come death and set me free
I've suffered so for you.