As a Kilkenny man I can give you one answer, which I heard from a trad duo un Kytelers Iinn there about 8 years ago. They assured me it originated from an English chap, a sort of minstrel, who would come over to Ireland regulary and drift from town to town singing for his supper, usually made his way down from the north to Kilkenny where he lost his heart to a local girl and vowed to wed her. It's unclear what exactly became of him except he went away and became ill and presumably died. The marble as black as ink line refers to the fact that Kilkenny is built upon the finest reservor of lmestone in Europe, and particularly famed for it's black marble, which adorns many of the pubs and churches in the town, perhapd our minstrel carved his and his love's names on the marble. Might help to tell you I grew up in Ireland in the 5's and never heard this song till the 60's, dspite my grandmother being a fine trad musician and held weekly trad nights, I never heard it sung there. So that could support the theory that Behan wrote it

Desi C