Complex sentence: The song is written in the form of a letter from "L. Cohen" to a mysterious unidentified "you," who seems to have been involved in a love triangle with Cohen's woman, Jane.
Split into simpler sentences: The song is written in the form of a letter from "L. Cohen" to a mysterious "you" who is never identified. "You," whose gender is never made clear, seems to have been involved in a love triangle with Cohen's woman, Jane.