God has never done anything that should legitimately cause anger in any of His children. We are never warranted in getting angry at God. Ever. It happens. And we should admit it, and tremble, and repent, and turn back to humble trust in His sovereign goodness.
All understandings of all things that do not take God into consideration are superficial understandings, since they do not reckon with the true deepest connections with all things with what really matters in the universe, namely God. We today in America can scarcely begin to feel how God-ignoring we have become because it is the very air we breathe. We breathe God-ignoring air.
The assurance of the believer is not that God will save him even if he stops believing, but that God will keep him believing–God will sustain you in faith, he will make your hope firm and stable to the end. He will cause you to persevere.