to bust or not to bust?

What would you do if somebody really close to you did something wrong? Are you going to bust them right away or wait for the right moment to do so? But, you know that the longer it takes to bust that person,the more the person will do the wrong thing. Just say you found out that your closest friend is out there gambling like a mad man, would you bust him or her right away or would you keep it a secret? Yes, I know that the right thing to do is to bust them as quickly as possible but is it that easy? You know that your friendship is on the line but it will be wrong to leave him just like that. I'm at a cross road.