The Cassidys have been together for 28 years, married for 23 and have a 23-year-old son. They have been living separately for about four months.
"This has been looming for some time," Sue told TMZ Monday. "I am truly heartbroken that our marriage is ending."
The celebrity news website said Sue declined to divulge whether her decision to divorce David is related to his ongoing battle with alcoholism, but she did say, "I'm glad David is getting the help he needs and I am confident he will come back better and stronger than ever."
David, 63, was arrested last month in Los Angeles for driving under the influence of drugs or alcohol, and is currently in rehab undergoing treatment for addiction, the celebrity news website said.