Confidentiality is a key principle of good small groups. People need to be able to share honestly and vulnerably without worrying that what they share will be blabbed to others! Talk about trust and the need for confidentiality in your group. Make sure everyone is committed to loving one another enough not to repeat to others what someone shares. Honor one another by creating a place where people can be real and ministered to when they open up because they know your small group meeting will give them the safety to do so.
When people in a small group break confidentiality it can damage a group because it destroys the trust that is needed for community to grow. If this ever happens, take it seriously and call the offender to confess and make things right with the one they offended as well as to the entire group. Healthy small groups are safe places where the people are committed to be real with each other. For that to happen, they must trust each other!