"Never does the Bible talk about the idea of “forgiving yourself.” We are told to forgive others when they trespass against us and seek forgiveness. When we ask for God’s forgiveness based upon Christ having already paid for our sins and our having trusted in Him as Savior and Lord, He forgives us. It is as simple as that (1 John 1:9). However, even though we are released from the bondage to sin (as spoken of in Romans chapters 6-8), we can still choose to wallow in it and act as though we are not freed from it. Likewise with guilty feelings, we can accept the fact that we are forgiven in Christ, or we can believe the devil’s lie that we are still guilty and should therefore feel guilty.
The Bible says that when God forgives us, He “remembers our sins no more" (Jeremiah 31:34). This does not mean that the all-knowing God forgets because He forgives us. Rather, He chooses not to bring up our sin to Himself or others. When our former sins come to mind, we can choose to dwell upon them (with the resulting guilty feelings), or we can choose to fill our minds with thoughts of the awesome God who forgave us and thank and praise Him for it (Philippians 4:8). Remembering our sins is only beneficial when it reminds us of the extent of God’s forgiveness and makes it easier for us to forgive others (Matthew 18:21-35).
Sadly, there are people who don’t forgive themselves because they really don’t want to forget their former sins, choosing rather to continue getting a vicarious thrill out of reliving them in their minds. This, too, is sin and must be confessed and forsaken. A man who lusts in his heart after a woman is guilty of the sin of adultery (Matthew 5:28). In the same way, each time we mentally relive our sin, we commit the same sin over again. If this is happening in a Christian’s life, the pattern of sin/guilt/sin/guilt can be destructive and never-ending.
Remembering that our sins are forgiven should make it easier to forgive others their sin (Matthew 7:1-5; 1 Timothy 1:15). Forgiveness should remind us of the great Savior who forgave us, undeserving though we will always be, and draw us closer in loving obedience to Him (Romans 5:10; Psalm 103:2-3,10-14). God will allow our sin to come to mind (Satan may intend it for an evil purpose, but God allows it for a good purpose), but He wants us to accept His forgiveness and rejoice in His grace. So, the next time your former sins come to mind, “change the channel” by choosing to dwell upon His mercies (it might help to make a list of verses that encourage you to praise) and think about how we should loathe sin."
(the above is from GotQuestions.org