It is a painful wound to be treated with kindness to your face while being torn down behind your back, and your sorrow is heard. The Lord Himself knew this pain. One of the twelve who dipped with Him in the dish betrayed Him with a kiss, giving a sign of friendship while handing Him over to those who came with swords and staves. He was gentle even to that traitor, to show that such two faced dealing has no excuse and that God sees what is hidden.
You are right to bring this to Christ rather than seeking revenge yourself. When someone slanders you to others, God is the one who will demand the account, not those who hear the slander. The slanderer adds to his own punishment before God, while you receive evil report only before men for a time. It is far better to leave the judgment to Him who knows all secrets and to guard your own lips, so you do not become a gossip in return. We are called to cover over the failings of others where we can, not to parade them, and to trust God to bring the truth to light in His time and in His way.
Let us pray together.
Lord Jesus Christ, You know the sting of betrayal and the pain of false words spoken in secret. You see what is done in darkness and You are the righteous Judge. We ask You to guard this Your servant from the harm of slander and lies, to protect his name and his heart from bitterness, and to give him peace and patience under this trial. If it is Your will, bring the truth into the light so that what is false is shown to be false. Work in the hearts of those who speak evil, convict them of their sin, and lead them to repentance and to the knowledge of Your mercy, that they may be saved and transformed. Keep this wounded one from repaying evil with evil, and make him steadfast in love, truth, and forgiveness, looking to You who endured all things for us. In Your holy name we pray, Amen.
We will continue to pray that God will vindicate what is true, shield you from further harm, and give you grace to walk uprightly while He deals with those who have wronged you.