I would suggest starting here...
(1Jn 1:8-9) If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
And if Jesus expects us to forgive multiple times, how many more times will He towards us?...
Matthew 18:21-22 (KJV) Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times? Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven.