The dude is Bob Dylan, as I guess you know.

Yes, Joan Baez's song "Diamonds and Rust" is widely understood to be about her relationship with Bob Dylan, though he is not explicitly named in the lyrics, with Baez herself confirming this in her memoir.

Here's a more detailed look at the song and its connection to Dylan:

Inspiration:

The song was written after Baez received an unexpected phone call from Dylan, prompting a flood of memories and emotions about their past relationship.

Timing:

The song was written in November 1974 and released in April 1975, about a decade after their relationship ended.

Baez's Memoir:

In her memoir, "And a Voice to Sing With," Baez uses phrases from the song to describe her relationship with Dylan, explicitly stating that he was the inspiration for the song.

Rolling Thunder Revue:

Baez recalls telling Dylan that the song was about her husband, David Harris, when they were discussing songs to perform on Dylan's Rolling Thunder Revue tour. Dylan seemed surprised and asked "For your husband? Who did you think it was about?" Baez answered "Yeah. Who did you think it was about?" and Dylan responded "Oh, hey, what the f–k do I know?"