Asking for forgiveness is an act of humility and it is common for humility not to be easy for those who fall within the parameters that psychology recognizes as "balanced personality".
We all have a little bit of arrogance inside, a little bit of "believe better," smarter and less wrong than everyone else. These elements are part of the breeding ground that we are. So recognizing that we're wrong, lowering our heads, slamming it and asking for forgiveness, means hearing that voice that quietly yells inside us: You got it, you got it wrong! and that we often shut up or send too far.
Asking for forgiveness forces us to take an inward journey and tour the scene again, seeing it from an external plane, hand in hand with what we call objectivity, and that inside if it exists. Accept without excuses that we were wrong, that we were miserable with the other, that we assaulted him in a baseless defense, process all the emotions that this arouses and recognize ourselves guilty. From there it is to gather humility and ask for forgiveness. I'm sorry you should listen to each other's pain and wound and put up with it.
Now, apologizing is not firing a magic shutter on the other so that it forgives instantly.
Forgiveness is a process. It is also a journey inwards a journey to see face to face and face the pain, to recognize the damage that is inside, to understand that that damage is mine only and that no matter how tempestuous my emotions against the other, no matter how angry, hatred and spite I deal , that only harms me and those who affect my feelings. To understand that the only way to get that damage is forgiving.
The other, the one who asks for forgiveness, has to wait with patience and humility. You have to wait for the other to face your emotions and finally understand that forgiving is the formula for moving forward.
And one last thing, but very important. Being forgiven does not mean that we remain friends or live together, even if we are killed by the pain of loss.