We are truly sorry to hear about the pain you are experiencing, ###. We will pray with you and seek God's will for your situation. Firstly, let us address a few points.
First, let us clarify the term partner. This man is not your husband. You see him as your husband which is a legal and spiritual position not to be taken lightly. Marriage is a lifelong commitment between a man and a woman, as ordained by God Matthew 19:4-6. It is important to recognize that living together and seeing someone as a spouse does not make the relationship a marriage. The Bible tells us not to be involved in situations of sexual immorality. Consider this: Do you not know that he who joins himself to a prostitute becomes one body with her? For He says, The two will become one flesh 1 Corinthians 6:16.
Secondly, we note that the other woman was not mentioned as his spouse either. If she is not his wife, then the relationship is adulterous and he needs to separate from the other woman. God's word tells us not to covet another person's spouse Exodus 20:17. We are to flee from sexual immorality 1 Corinthians 6:18. The seventh commandment instructs us You shall not commit adultery Exodus 20:14. Therefore, we pray that he severs all ties with the other woman.
1 Corinthians 5:11 tells us to not associate with anyone who is called a Christian and lives in sexual immorality. Further, it is stated that if anyone causes one of these little ones who believe in me to stumble, it would be better for them to have a large millstone hung around their neck and to be drowned in the depths of the sea Matthew 18:6.
Thirdly, we notice that Jesus Christ is not mentioned in your prayer. Jesus is the only way to approach God. Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me John 14:6. We are to believe in Jesus Christ as the son of God and the savior of the world.
This is a difficult time for you, and we encourage you to turn to God for comfort and guidance. Remember that God is close to the brokenhearted, and saves those who are crushed in spirit Psalm 34:18. We encourage you to seek godly counsel and support from your local church community and Christian friends.
Let us pray together:
Dear Heavenly Father,
We come before You today, lifting up ### in her time of deep pain and need. We pray for her healing and comfort, and ask that You surround her with Your love and peace.
Lord, we pray for the man in this situation. We pray that he would leave this adulterous relationship and the other woman. We pray that he would come to true repentance for his actions, and that Your will be done in his life.
Father, we pray for reconciliation if it is Your will and for more than this, we pray for a miraculous restoration of all parties involved to a right relationship with You.
We pray all this in the name of Jesus Christ.
Prayer Focus: God, Thank You for loving me. Thank You for loving me, Jesus. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, soul, mind, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
