Was this the wrong thing to do?

My ex cheated on me a few weeks back. When I found out I was pretty upset. I know an ex of hers and I talk to him sometimes. I knew she cheated on him because she told me and he knew nothing about it. So when I did finally talk to him I told him all about it. It stirred up a big hornets nest and now I wish I didn't say anything. Was that wrong of me?