Complex sentence: Coolidge previously had romantic liaisons with Stephen Stills and Graham Nash; leaving Stills for Nash has been cited as a contributing factor behind the initial 1970 breakup of Crosby, Stills, Nash & Young.
Split into simpler sentences: Coolidge previously had romantic liaisons with Stephen Stills and Graham Nash. Rita leaving Stills for Nash has been cited as a contributing factor behind the initial 1970 breakup of Crosby, Stills, Nash & Young.