Admitting that you have said or done something in error can be more difficult when the other person is being overly sensitive. If that other individual happens to be your girlfriend, you are probably weighing approaches that will allow you to own your mistake in a way that doesn't make her more emotional. Taking an objective approach -- and not internalizing your girlfriend's reaction -- can help you deliver a sincere apology.
Acknowledge what you did or said that offended your girlfriend. The simplest thing to say may be “I’m sorry,” but explaining your transgression can have more impact. This can also provide your girlfriend with the opportunity to clarify her feelings and the event that led to them. Avoid the use of “you” in your apology. Instead, stick to explaining what you did by using “I” statements: “I am sorry that I didn’t call you when I said I would.”
Stick to the basics. Don’t assume you know how deeply your girlfriend has been affected. Mention how badly you feel. For example, “I feel horrible. I know it disappointed you when I didn’t call.” Don’t defend your actions. Remain calm to help your girlfriend process what you have said. Allow time for response and don't add information if you are faced with a strong emotional response or awkward silence.
Assure her that you will try not to make the mistake again. Don’t promise perfection. You’ll be setting yourself up for failure. Instead, explain actions you will take to reduce the chances of making the mistake again. This is best accomplished in person. Expect that your girlfriend may have different ideas about how you can change your actions. Tell her, “I realize that I lose track of time and forget to call. In the future, I will make a note to remind myself.” Your girlfriend, may continue to express strong emotions connected to your original actions. Remain calm in your discussion.
Forgive yourself and forgive your girlfriend. Beating yourself up isn’t helpful and can change the dynamics between the two of you. Remind yourself that you didn’t intend to hurt your girlfriend. Avoid reacting to any anger or resentment she expresses.Keep forgiveness in mind, regardless of her responses.