Is calling God unjust, unfaithful and stuff like that forgivable?
Calling God unjust, unfaithful etc simply shows that you don't understand God's part in life, and yours in particular.
God understands that this is a common problem, and He (my own feeling of God as a Fatherly Spirit Energy) is most likely disappointed but forgiving.
It's easy to blame God for everything that goes wrong or happens in a different way to what we'd choose.
We each chose the type of learning journey we needed to experience in this life. We chose challenges, and even if part way through we want to back out of them, God cannot interfere because it would be against what we agreed with God.
We see loved ones suffer, and we may wish God would take away the pain, but those people chose to experience that in order to develop their understanding.
Many people suffer in the world, and it's part of the human race's work here to help in the world. But too often we focus on our own needs rather than helping where it's needed.
It's sad that God is not understood better because without God's power and wisdom, we are very underpowered.
I suggest that you knock down any barriers of intolerance, and become more aware of what your instincts tell you, because that positive encouragement and guidance is God working with you through your soul.
Trust me, He's your greatest Friend.