Forgiveness does not absolve accountability, and when talking about self forgiveness, we actually have control over our own accountability. It’s one thing to validate one’s actions, and it is an important first step, but once the reason for one’s behavior is identified, the next step is to do something about it. You gave the example of infidelity connected with drinking. It’s likely that the real cause for these behaviors lies deep within the person and is something they don’t want to face, because they believe that it will validate that they are a terrible person. That’s where a good therapist can be of tremendous help. Excavating emotional traumas while removing guilt and shame is a powerful process that can take away the power of these past emotional traumas and heal the source of these harmful behaviors. I believe this is a necessary part of truly forgiving oneself.