The late Lewis Smedes in his book, Forgive and Forget, suggested that God is big enough to take our resentment and our forgiving. I am a great admirer of Dr. Smedes, but I think he got this one wrong. As you say, a perfect God cannot be unjust. If we presume otherwise, this can open up many errors in theology. For example, God is imperfect in this scenario and so why follow the imperfect? God is capable of sin in this scenario. Would you want to worship a sinful being?
Instead of forgiving God, I recommend working on acceptance—-acceptance of God’s will. Sometimes this involves suffering, but out of suffering can come strength, patience, and a deep empathy for those who suffer.