Betrayal is one of the worst things that can happen to you. To take someone into your inner circle of confidence and then to have him turn upon you hurts worse than any enemy's attack. Jesus knew intimately this pain of betrayal as He watched Judas walk out into the night to fulfill his wicked plan (John 13:30). David also faced betrayal when his commander-in-chief Joab secretly murdered Abner (2 Samuel 3:27).
When a trusted ally treats you with contempt, you may want to retaliate in anger. David refused to exact revenge upon Joab. He knew Joab would eventually reap the fruit of his betrayal and thus pronounced Joab cursed in all his generations. Jesus turned Judas over to Satan so that Judas would reap the terror of betraying the innocent. Instead of retaliating, Jesus even washed Judas's feet before Judas left to betray Him! On the cross, Jesus epitomized the essence of true forgiveness when He said, "Father, forgive these people, because they don't know what they are doing" (Luke 23:34).
Forgive and release your betrayer to God so that He may deal with him. If God is for you, who can ever be against you (Romans 8:31)?