I forgave my ex-partner and all was forgiven and forgotten. This was years ago. All of a sudden, I find myself angry all over again after three years. Did I not go through the forgiveness process the first time?
Forgiving others is not a perfect straight line that gets you to the end of anger and then all anger is finished. The late Lewis Smedes said that forgiving is an imperfect process for imperfect people. Sometimes anger does resurface and it is good to once again go through the forgiveness process. This time, it likely will be a shorter journey, well worth your time and effort. Anger does not necessarily go away completely and so please be gentle with yourself as you forgive again. You may have to do this in the future and this is not unusual.
For additional information, see Forgiveness for Couples.