Complex sentence: Insiders in Hollywood later said that Lawford's extramarital activities and Kennedy's strict principles led to divorce; in addition, Lawford had a fight with Sinatra, and he found himself out of the Rat Pack.
Split into simpler sentences: Insiders in Hollywood later said that Lawford's extramarital activities and Kennedy's strict principles led to divorce. In addition, Lawford had a fight with Sinatra, and he found himself out of the Rat Pack.