The process of forgiveness begins with a sincere apology for causing pain, but an apology is insufficient if the pain is great. Then you must be able to show you understand just how much your partner is hurt. If you fail to show sufficient empathy, then your partner will be tempted to dramatize the pain to get you to see how much hurt you have caused. Even worse, your partner may be tempted to cause you pain so that you can appreciate the pain you have caused.
Forgiveness requires the hurt partner to be willing to share pain in a vulnerable tone and to be willing to accept soothing for the pain. The process can be blocked indefinitely if one holds onto the pain. One reason to hold onto the pain is that it has traumatized you and it is difficult to absorb the reality of the action. But another reason to hold onto the pain is to avoid the risk of regaining the closeness you once had, then risking further pain. In this way, pain is a protection from further pain, but also a barrier for regaining emotional intimacy.
If you have hurt your partner, be strong enough to go down the path of understanding your partner's pain instead of defending your actions. If you have been hurt, be strong enough to share your pain, but allow your partner to be soothing so that you can be forgiving. Forgiveness is a process not a choice. Both of you must be patient enough to wait for the pain to recede and the desire for connection to emerge.