I am a Christian (Protestant)--What I've found in the Word is that there is no act so terrible that the power and saving blood of Jesus Christ can't save.
Please read the story of David who named "a man after God's own heart."----After God lifted him up and anointed him as King of Israel, he went after a woman by the name of Bathsheba. She was the wife of his most trusted army general, Uriah. When she became pregant (I think this the way the story goes..)--David didn't know what to do. So to hide his sin and "do the right thing by Bathsheba"--he sent Uriah into battle and ordered him to go on the front line. Of course Uriah gets killed. David marries Bathsheba.
Nathan the prophet of God who lived in the palace--prophesied that David would pay for his sin.
When the child was born, it did not live long. David repented and wrote the Psalm 19. Because he repented, fasted and prayed, God forgive him and he and Bathsheba had another child, a son by the name of Solomon. Solomon was the wisest king ever to rule Israel.
In summary, David committed adultery, murder, covetousness, and he downright lied. God forgave so He will forgive you too.
The bible is filled with many stories of people of faith--Saul persecuted the new Christians--murdering and torturing. God literally knocked him down on a road called Damascus, blinded him for three days. When that happened, he was given a new name. Paul. The apostle Paul's letters account for much of the New Testament. Protestants and Catholics alike use his letters as the basis for living.
Here's another one: Two thieves were hanging next to Jesus recognized his divinity as they were being crucified. The first thief wanted to Christ to save them, since He was God. The second thief wanted no such thing but wanted to Jesus to simply remember him in paradise. Jesus saved the second man even as he was dying on the cross.
I pray this helps you in your journey. Please read Psalm 19 and Psalm 139. When I felt guilt ridden, I found these two texts to be of great help. Please let me know if I can be of assistance.