Have you ever told someone a secret and asked the other person to not tell only to find out that several people have the information that you wanted to be protected? How did you feel about that? I bet you were hurt and shocked and angry. You also likely decided that the person who you trusted is no longer trustworthy.
Well that is how clients feel when you offer confidentiality and then do not honour it. They gave you their trust when they told you their story and shared information with you but, now that they know that you will not honour the promise that you made to them, they will likely no longer give you their trust. And, in fact, they will likely be more hesitant in trusting anyone in the future. That is why there are specific ethical guidelines that lay out expectations regarding confidentiality and why regulatory bodies treat a breach extremely seriously.
It is more than just going to talk with someone else about the confidential information though. A client may feel that you are not protecting their confidentiality before they even leave your office. If they can hear voices of people in the next room, they will assume that their conversation can be heard. If they hear you talking about another client over the phone, they might think that you would talk about them in front of other clients. If you leave a file within eyesight, they might think that you will leave their file so other people can see it. If they even hear you share information with another staff member in front of them, they might think that you are not worthy of their trust.
You see, most people have things that are very private and do not share these with other people easily. If they are willing to come to you in order to resolve issues and place their faith in your professionalism, then you need to make sure that you deserve their trust. One of the easiest ways to do this, is to never tell anyone about what you hear. That way you have control over the information and do not risk having the information spread by someone else. You see, if you don't tell anyone, there isn't any chance of you being involved in a breach. Make sure that your environment and your actions are ones that will help your client's trust to build and you will earn their respect and likely receive referrals from them because of this.