James didn't believe his brother could be the Son of God. He even took his mother to try to convince Jesus to return home. He felt Jesus was crazy or deluded. Jesus made a special effort to go to him after His resurrection. James faced his brother and received Him as Lord and Savior. James became known as 'camel knees' because he spent so much time praying to and communing with his brother. He became one of the great leaders of the early church.
Peter's story is well known. He denied the Lord. He rebuked the Lord for telling what would happen in the future. Like many of us, he didn't want to hear bad news. Yet after it all, Peter was willing to die for the Lord. He believed gaining eternal life was worth the cost of spreading the gospel.
So many of us have made mistakes, big and small. Yet none of the mistakes we have made can take us away from the loving forgiveness and compassion of Jesus. The only thing that can separate us from Jesus is our own choice to walk away. He stands waiting for us to return. If Paul, who killed the early Christians can be used to evangelize the world, we can be used to serve in whatever way the Lord sees fit to use us.
I have heard so many say that the Lord can't forgive whatever sin they committed. They are either making the Lord very small or they are overestimating the importance of their sin. Keep the Lord and His forgiveness in perspective. His ways are so much higher than ours.
Press on toward the heavenly goal. Accept His forgiveness and strive to serve Him with all your heart and mind and strength. Learn from the past, don't live in it. You will miss so much of what God has for you in the here and now.