How long wilt thou forget me, O Lord ? for ever? how long wilt thou hide thy face from me? [2] How long shall I take counsel in my soul, having sorrow in my heart daily? how long shall mine enemy be exalted over me?
Psalm 13:1-2 KJVS

How long will thou forget me?
Often scripture would say that God remembered: And I have also heard the groaning of the children of Israel, whom the Egyptians keep in bondage; and I have remembered my covenant. – Exodus 6:5
Did God forget his covenant? His Word? Not at all. Saying he remembered is saying that the time has come. So the question should be: What time has come? Before we answer that, let’s first address what it means to be forgotten.
What does it mean to be forgotten?
To be forgotten of God communicates death.
I am forgotten as a dead man out of mind: I am like a broken vessel.
Psalm 31:12
For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten.
Ecclesiastes 9:5
God did not forget (in the way we understand) those who trusted him and died. We know this because Christ CAME FOR THE DEAD, to redeem THEM & US from it (death) and to destroy death in the process:
I will ransom them from the power of the grave; I will redeem them from death: O death, I will be thy plagues; O grave, I will be thy destruction: repentance shall be hid from mine eyes.
Hosea 13:14
To do the above he had to enter the land of forgetfulness, the dwelling place of the dead i.e. in and under the earth. And there were his wonders seen.
[10]Wilt thou shew wonders to the dead? shall the dead arise and praise thee? Selah.
Psalm 88:10-12
[11] Shall thy lovingkindness be declared in the grave? or thy faithfulness in destruction?
[12] Shall thy wonders be known in the dark? and thy righteousness in the land of forgetfulness?
The coming of Jesus moves man from forgotten to remembered, from dwelling in death to dwelling in life.
David asking the question “how long will you (God) forget me”, is him asking, “when are you coming? When will you deliver your people?”.
The answer is: in the coming of Christ.
Recommended reading Psalm 13:1 how long wilt thou hide thy face from me?
For you and I today, if we are forgotten (dead), it because we chose to be. God has already remembered his covenant and provided himself for an offering on the cross (Gen 22:8).
We are beneficiaries of this (his sacrifice) when he comes into our lives. If we choose to forget him, that is, live a dead life, we will remain eternally separate from him (dead).
God has remembered you, will you remember him?