Traded my artist and I pawned off the easel
He has traded the musician inside of him for liquor.
Literally speaking, an artist (e.g., a painter) might have to sell his or her tools to a place like a pawn shop, where one can receive loans by giving collateral, to sustain their alcohol addiction due to their lack of finances. Telling from the rest of the song, he might not get that easel back.
Figuratively, he has sold his potential and what makes him who he is as an artist for the alcoholic in him.
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