So with a bit of googling. Charlie can be a slang term for idiot and other such synonyms in Gaelic. As to the lyric in plain English, it could be read "young Monroe, be my idiot/fool. Young Monroe, I do love you. Young Monroe, young Monroe, be my idiot/fool. Handsome idiot/fool, young Monroe.

http://www.peevish.co.uk/slang/english-slang/c.htm and https://en.m.wiktionary.org/wiki/Charlie

charlie        Noun. 1. Cocaine. Probably the most commonly used slang term for this drug.
2. A fool, an idiot. Also charly.