God forgives and forgets. Amazing, isn't it? He remembers everything you've done right while forgetting everything you've done wrong. Yet, while God cannot remember our confessed sin, we have a much harder time forgetting it. We tend to remember our mistakes more readily than our successes. That's why it's harder to forgive ourselves than to receive God's forgiveness. We tend to remember what we should forget while forgetting what we should remember. That inability to forget the sin we've confessed is part of our sin nature itself. The fall fractured the image of God in us, including the amygdala: that's the part of the brain responsible for storing emotional memories. The strength of the memory is dictated by the strength of the emotion. We quickly forget the moments that don't make a blip on our emotional radar. Strong emotions, such as shame, take sinful snapshots and poster-size them. They get blown out of proportion in the darkroom of the mind.
Are you struggling to forget what God has forgiven? Read these Scriptures prayerfully: 'I, even I, am he who blots out your transgressions for my own sake; and I will not remember your sins' (Isaiah 43:25 NKJV). 'I have blotted out, like a thick cloud, your transgressions, and like a cloud, your sins. Return to me, for I have redeemed you' (Isaiah 44:22 NKJV). 'For I will be merciful to their unrighteousness, and their sins...I will remember no more' (Hebrews 8:12 NKJV).
God has forgiven and forgotten your sin - it's time for you to agree with him and do the same thing.