Smith became an employee and then mistress of Lightfoot in the early-to-mid 1970s. At one point, she even drove the tour bus. Smith sang backup on Lightfoot's song "High and Dry" which was on the Sundown album. She apparently sang more backup on the album but Lightfoot mixed most of it out.
By several accounts, the affair was volatile and illustrated in the lyrics of "Sundown," Lightfoot's only Number One hit and his most financially lucrative song. It reflects the dark feelings Lightfoot was experiencing at the time. Drinking too much and married to another woman, he on one occasion broke Smith's cheekbone in a fight. Lightfoot has stated of his three-year relationship with Smith, "I was sometimes crazy with jealousy."
Bluegrass musicians Bruce and Brian Good, The Good Brothers, who were one of Lightfoot's opening acts during that time, got fired by Lightfoot for "flirting" with Smith. Smith was cited in divorce papers, and shortly after his affair with her ended, Lightfoot was a party to the most expensive divorce settlement in Canadian history to that date.
In a 1975 interview, Lightfoot expanded upon Sundown and hinted at the worry he experienced in his relationship with Smith:
All it is, is a thought about a situation where someone is wondering what his loved one is doing at the moment. He doesn't quite know where she is. He's not ready to give up on her, either, and that's about all I got to say about that."
Lightfoot gave another insight into his relationship with Smith in a 2000 interview when he remarked upon "Sundown" being:
"a back-alley kind of tune. It's based on infidelity -- I've seen both sides of that."
http://en.wikipedia.org/wiki/Cathy_Smith