God’s Word speaks to His intimate knowledge of us. He knows every day of our lives, from conception to grave. (Psalm 139) And yet He came anyway. “…but God shows his love for us in that while we were still sinners, Christ died for us.” (Romans 5:8, ESV) Our Lord is not surprised by our sins. Not past, not present, not future. There is not one thing that has escaped His attention. It is still important to repent and ask forgiveness of our sins, even sins long forgotten. Memories of our transgressions get stirred up and come back to mind days, months, or even years later, BUT, do not dwell there.
The Lord is merciful and gracious, slow to anger and abounding in steadfast love. He will not always chide, nor will he keep his anger forever. He does not deal with us according to our sins, nor repay us according to our iniquities. For as high as the heavens are above the earth, so great is his steadfast love toward those who fear him; as far as the east is from the west, so far does he remove our transgressions from us. As a father shows compassion to his children, so the Lord shows compassion to those who fear him. For he knows our frame; he remembers that we are dust. (Psalm 103:8-14, ESV)
Although we are walking out our sanctification, always remember that ~ through Christ's sacrifice on the cross ~ we are completely justified before God the Father. Regret and repentance, is a part of acknowledging our own sin, but we should not remain there. Christ's claim on the cross, "It is finished" (John 19:30) says it all.
We are to repent, we are to confess our sins (1 John 1:9), and we are to grow, but we are to move on. If God has forgiven our sins and removed them “as far as the East is from the West”, we need to keep moving on, just as Lott and his family did while fleeing Sodom and Gomorrah.
The sun had risen on the earth when Lot came to Zoar. Then the Lord rained on Sodom and Gomorrah sulfur and fire from the Lord out of heaven. And he overthrew those cities, and all the valley, and all the inhabitants of the cities, and what grew on the ground. But Lot's wife, behind him, looked back, and she became a pillar of salt. (Genesis 19:23-26, ESV)
And so God will deal with all of the sin in our lives. Once He moves us forward… never look back. We cannot change the past, we can only learn from it.