|Some people try to make themselves appear big and powerful by revealing confidential information, but the reality is that they are revealing their big powerful personal insecurities. It would be nice to never share anything confidential with this manager again, but if there are matters that require his input, it sounds like you cannot permanently shut him out.|
You should meet with him to express your concern. In this meeting, do not fill your comments with “you” words, such as, “How could you?” or “Why did you?” You are likely to have a more productive conversation if you use “I” words, such as, “I am puzzled how the confidential information we discussed fell into so-and-so’s hands.” The next step is to listen.
If he proffers up an acceptable explanation, the case is closed. If he falls short, you should express your concern and dissatisfaction, and then ask how you can work with him to prevent this from happening again. Regardless of his pronouncements, you should be extremely discreet in what you say to him for the foreseeable future.
If he develops the reputation of an individual who cannot keep confidences, he may well find that management loses confidence in him.