To add to Eugenia's good explanation, although it had a specific meaning in that song, it's not a commonly used expression with a clear meaning.

The phrase "stupid cupid" relates to the lyrics of the song "Stupid Cupid" recorded by Connie Francis, suggesting that love can interfere with scholastic efforts, and distract from studies. Another meaning might be that Cupid (God of love in Roman mythology) chooses the wrong person as an object of someone's love, and in this sense it might be a synonym to "love is blind" phrase.