I think a lot of it has to do with pride, and a few lies we believe in.
When I feel like I cannot forgive myself, usually it is one of the following:
I believed I have done something unforgivable, either a terrible deed, or how quickly and stubbornly I went back to it after confession, or I simply no longer planned to stop committing it even when I was confessing it. All these basically are saying: God’s word of forgiveness is not enough. I am beyond repair even for God. This is pride, because that’s saying that I am greater than God; or it’s not what You say that counts, but what I say. No, if God says He forgives you, you are forgiven. We need to accept that. Anything contrary to it is simply not true, and so cannot be from God. I must renounce that falsehood.
Secondly: but I still “feel” ashamed. What actually is going on though, is rather I feel I need to be good enough before I can stand before God. It is knowing that I’m so broken and sinful and imperfect, that I can’t stand myself. This again is pride. This kind of thinking is built on the premise that I need to merit GOd’s acceptance. But that is simply not true for two reasons. First of all, it is precisely because we are completely hopeless in saving ourselves that Jesus came to die for us unconditionally while we were still sinners. To think that I’m good enough for God only when I can be good myself is a heresy known as Pelagianism. (Look it up.) we cannot restore our relationship with God. Without God’s grace, we are completely hopeless. Thanks be to God, He loves to abandon 99 righteous men to come after me. He made me acceptable and delightful to Him even when I’m still a sinner; ugly and broken in my view, He embraces and kisses me as the father to the prodigal son.
The second reason: we don’t need to earn our identity before God to begin with. I’m GOd’s child, by His breathing His image and likeness into me and by baptism. Nothing I have done and nothing I will do can change that. God loves me, as I am His child, always. His love for me is not because I’m fixed up. It is because I’m His, and He is mine. I need to accept that yes I am a broken sinner, but I am a redeemed sinner, redeemed by His Blood, loved by Him eternally. That is the good news, the great news, the free gift of salvation from God, that He is the loving Father that always loves me because it is my identity: I’m His child, and for that He wipes away my sins, no matter how many times.
At he end, I need to accept that I am okay to be not okay, because He is okay with me.
Of course, it is not okay to stay in sin. But it is no longer me trying to earn back alone n identity I never lost to begin with, but instead leaning on my good Father and asking for His blessings to fight another day with Him.