Ask yourself these Five Questions first:
1. What is your intent?
2. Is it really to protect him or is it to save yourself grief?
3. What if the truth will only hurt him?
4. Will he find out from someone else?
5. Do you have a right to your privacy?
An argument can be made for keeping your own confidence. In the same way our friends trust us with their secrets we can feel OK keeping certain things to ourselves.