To forgive in one context, let us call it Situation A, does require that you reduce the defense mechanisms that prevent you from seeing the depth of your own hurt and anger. This can be done slowly and gently.
Your having lowered those defense mechanisms in Situation A does not mean that you will have lost your natural ability to have defense mechanisms in the future. In other words, breaking denial in Situation A does not mean that denial will not operate well in Situation B. Denial still will need to be slowly lowered in Situation B if that denial is not allowing you to see that you are angry, that the anger is compromising your well-being, and that you need to do something about that anger.
Read more about dealing with defense mechanisms in Forgiveness Is a Choice.
A person need not tell others that they are forgiven. Yet, if you wish to bring this into the open, I first would wait until the other is in a good mood before bringing this up. I would start gently by saying something like this (presuming that the context is one in which you would like reconciliation): “I respect you and like you. May I say something about Incident X in which we had that argument?” I then would not go into any details of Incident X and instead talk of your positive feelings and thoughts relative to forgiving.
Yes, you make a good point. Anger, indeed, can be a defense mechanism in the form of displacement. A person displaces an emotion onto another so that the real issue remains hidden. So, the psychological defense of denial can mask anger; displacement of anger can mask disappointment or embarrassment, as you say. Both anger and disappointment may need to be addressed in the same person.
Read more about defense mechanisms in Forgiveness Is a Choice.
To apologize is part of asking for forgiveness but does not constitute the entire process. Asking for forgiveness includes the development of remorse or inner sorrow. Then comes repentance or apology. Finally, there is recompense or trying one’s best to make up for what happened.
I find it interesting that in your last sentence you use the words “truly” and “fake.” These are contradictions. I truly think that you cannot fake forgiveness. Your girlfriend will see this in your behavior, which may include some annoyance or even disrespect. You obviously have your eye on the theme of forgiving. Why not give it an actual try?
Forgiveness, according to Aristotle, develops in part by practice and by the support of others for that practice. I suggest what we might call “teachable moments.” Suppose you are watching a film together and there is conflict among the characters. You could ask this of the adolescent: “What might have happened if Character A forgave Character B rather than seeking revenge?” Another teachable moment is at the dinner table when people may be talking about their experiences that day. If someone has had a conflict at school or at work, then discuss this with an eye toward forgiveness as still a possible option.
First, please keep in mind that you should not insist on their forgiving you because forgiving is that person’s choice.
Second, give the person time. That person may be angry and needs some time to process the anger.
Third, humbly and gently ask for forgiveness, knowing that the person may not be ready yet. Express regret as you ask for forgiveness. Try to make up for what you did, at least within reason.