Many people feel that Psalm 88 is the saddest Psalm.
It has no resolution.
Most Psalms that start with sorrow end with renewed hope in the Lord. But in Psalm 88, the Psalmist's outlook is the same at the end of the Psalm as it was at the beginning.
It's more a lament than a Psalm. A sad song.
It ends with this sad line: "darkness is my closest friend."
But several factors in the Psalm give us hope.
Despite his feeling that God is ignoring him, the Psalmist continues to seek God.
He knows that God is the one who saves (verse 1).
Job didn't write this Psalm, but he could have, and the book of Job gives us the resolution that this Psalm lacks:
God is good. Even when we don't feel His presence and don't understand our circumstances, God is good (Job 38-42).