Your friend trusted you with intimate details of her life or another matter that she considered private. Rather than keeping the information to yourself, you repeated it to someone else, violating your friend's trust. Admitting fault and apologizing for your indiscretion isn't easy, but an effective apology can be worth the effort.

Don't Wait to Apologize

When you become aware of the need to apologize to your friend, don't put it off. Approach your friend right away and let him know that you're sorry you upset him, suggests Sophie Keller, a happiness expert and author of "How to Make an Effective Apology" on the "Your Tango" website. Ideally, you should apologize to your friend in a face-to-face setting, where you can talk privately without interruption.

Acknowledge Your Mistake

It's important that your apology be sincere and that you're not apologizing just for the sake of apologizing. An apology that is successful requires an effort to understand the other person's feelings and an admission of fault and weakness for your mistake, says Aaron Lazare, a psychiatrist and author of "Go Ahead, Say You're Sorry" on the "Psychology Today" website. For example, you might say, "I am extremely sorry for telling Sue the intimate details of your breakup. It was not my place to share that information, and I shouldn't have done it. I'm sorry I betrayed your trust and hurt you." It's important that you are specific as to what you are apologizing for and indicate what you did wrong and how it impacted the other person, Lazare says.

Provide an Explanation

Another important component to an apology is providing a reason as to why you did what you did, Lazare says. For instance, you might say, "I wasn't thinking clearly when I told Tim that you flunked the test." The explanation should also make it clear that the behavior isn't characteristic of you and that what you did wasn't meant as a personal attack, Lazare says. For example, you might tell your friend, "I wasn't intentionally trying to hurt you." It's also important that you accept complete responsibility for your behavior. When apologizing, don't say, "I'm sorry that what I said upset you," rather say, "I'm sorry I upset you."

Ask Your Friend for Forgiveness

Ask your friend to forgive you and assure her that the behavior won't happen again. A person wants to be reassured that your behavior was an exception and the problem can be fixed, says John M. Grohol, a psychologist and author of "How to Make an Adept, Sincere Apology" on the "Psych Central" website. For instance, you might say, "Will you please forgive me for what I did? It won't happen again."