This particular song was written about Bob Dylan. They toured together in the 1960's, and they were also romantically involved. Here's a link to the lyrics.
I love this song because we all have times in our life that are like this, so full of beautiful and terrible memories, and sometimes they come back to us, playing over and over like a movie reel. I love that this song is so honest about this particular time in her life. She lays their story, her emotions all out on the table.
I'm also in love with her voice. I encourage you to go listen to some of her other music. She's really fantastic.