"But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit..." Titus 3:4-5
Let it go. I think we've all had a grudge we've held onto. Our spouse or friend or family member did something that hurt us. Maybe they apologized, maybe they didn't, but it's in the past. It's time to forgive and truly move on, because God's love has covered up those wrongs.
Being 'born again' is only the beginning of the story.
The Holy Spirit renews us each time we confess. And just because you've been born again, doesn't mean you stop sinning or needing to confess those sins.
But we can't dwell on those mistakes, those bad choices or habits. Instead, let's dwell on the incredible mercy of Christ.