The old section 121 publication restriction has now been replaced by Part XIVB of the Family Law Act. In broad terms, sections 114Q and 114R restrict publishing or communicating information about family law proceedings in a way that identifies parties, witnesses or others involved, for example by posting details on social media or a public forum. It is a criminal offence, not a civil wrong you sue over directly, so the appropriate recourse may include raising it with your solicitor, asking the court dealing with the family law matter to address the conduct, or reporting it to police for potential prosecution in a court with criminal jurisdiction.
Whether particular conduct actually falls within these publication restrictions can be a fine legal question. Sharing something with one or two specific individuals privately, rather than to the public or a section of the public, may not meet the threshold, even if it feels like a serious breach of trust. Because the wording and exceptions are quite technical, it's worth getting specific advice from a
family law solicitor on whether what happened meets the legal definition before deciding how to pursue it, since that will determine whether a police report, an application or complaint in the existing proceedings, or another remedy is the right path.
Disclaimer: Please note information in this response is general in nature and should not be treated as legal advice. It may not be complete or up to date for your specific situation. Independent legal advice is always recommended.