every time you see "leanndubh" in the chorus, it should be "lionndubh"

leann dubh is black beer, i.e. porter, stout

lionn dubh is depression, melancholy

The pronunciation of leann and lionn is fairly similar, hard to make the distinction. This database can help sometimes
https://www.teanglann.ie/en/fuaim/ but it doesn't have an entry for lionn!