The fear of being abandoned by God is a good fear. I will briefly explain why.
First:
A person who feels abandoned by God recognizes that there is a highest good, and that is correct. Being abandoned by the highest good is frightening because this good is irreplaceable. This thought, this feeling, is terrible, but good.
Second:
God, who is the absolute and perfect good, did not create us so that we would be lost or live without Him or be rejected by Him. Quite the opposite: He knows, even before you do, that you need His help. In acknowledging that you need God’s help, God is pleased to help you. You are His child, He is your Father. A father does not let his child go astray or leave them like an orphan. The Lord is close to the brokenhearted and the suffering. The thought of being abandoned is good, but also despairing if you believe it. The Lord never abandons any of His children. On the contrary: He wants all to be saved. That is why He sent His only begotten Son, our Lord, so that the world might be saved. You may and should know that God is near to you when you call upon Him. Give all your suffering to God. No, you are not abandoned. The Lord, your God, is always there for you, whether you feel it or not. This you should know.
Third:
Human weakness in difficult situations is real and challenging. But you should know that nothing in this world remains insurmountable. It is hard when you do not have God, but where humans cannot, the Lord helps. Everything you can do, the Lord leaves to you; but where you cannot, the Lord helps you, for without Him it would be impossible. This you should know and believe.
In conclusion:
Psalm 94:17–19:
If the Lord had not been my help,
soon my soul would have dwelt in silence.
When I say, “My foot is slipping,”
your mercy, Lord, supports me.
When the cares of my heart are many,
your consolations cheer my soul.