Jesus’ words to Judas, “Friend, why have you come?” must have haunted Judas from the time they pierced his ear drums. The words Jesus had spoken at the last supper must have come rushing back into Judas’ consciousness, “Woe to that man by whom the Son of Man is betrayed. It would have been good for that man if he had not been born.” Scripture says Judas tried to make up for his betrayal by returning the money the priests had given him to betray Jesus (Mt 27:1-4). His grief overwhelmed him to the point of committing suicide (Mt 27:5).
Peter denied Christ three distinct times yet Jesus said to Peter, “"Simon, Simon, behold, Satan has demanded permission to sift you like wheat; 32 but I have prayed for you, that your faith may not fail; and you, when once you have turned again, strengthen your brothers” (Luke 22:31-32). What made the difference between Judas’ response and Peter weeping bitterly (Mt 26:69-75)?
I do not understand fully the answer to this question. But we do know that Peter loved Jesus, but denied him out of weakness. Judas never believed in Jesus but only saw him as an opportunity to fill his pockets (John 6:64, 70-71; 12:3-6). Peter’s sorrow was that of repentance. Judas did not seek God’s forgiveness, but insisted on taking the punishment onto himself.
None of us deserve God’s grace, but he offers us forgiveness out of his abundant mercy (Ephesians 2:4-5).
