Unless there's some kind of protected relationship (e.g. attorney-client relationship), or some contractual obligation to secrecy (e.g. trade secrets), or some such thing, I'm not aware of any law that would be violated by simply showing someone else an email that you sent. In fact email communications are regularly disclosed to third parties and used as evidence in family court matters.
Unless you had previously obtained a court order that affirmatively prohibited disclosure of these emails to a 3rd party, your husband's sharing of them to "Cathy" or anyone else did not violate any laws.
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