Old Pal of My Heart

Somebody wrote to me about 'At Swim' the other day, and included these lyrics to a song I've never heard. It's an old country/bluegrass song and it gave me chills, reading the lyrics. Put that to an Irish melody, and you've got ( 'Old Pal of my Heart' )

(Needless to say, SPOILERS, so don't read unless you've finished.)