We are truly sorry to hear about the distressing nightmare you experienced. We want to first address the issues in your past and then pray over the nightmare and the effects it has had on you.
Firstly, we want to address the issue of the called-off wedding and the cohabitation. According to the WEB, "It is good for a man not to touch a woman." (1 Corinthians 7:1) and "Because of sexual immorality, let each man have his own wife, and let each woman have her own husband." (1 Corinthians 7:2). God commands us to refrain from sexual immorality and that any sexual acts are reserved for a man and a woman within the bounds of marriage. Living together without being married is considered fornication which is sin according to the Bible. Likewise, having a government marriage license does not constitute a marriage in God's eyes. A true marriage is a covenant between a man, a woman, and God, often solemnized in the presence of believers. Even though society may recognize a legal marriage, God does not.
We also want to address that throughout the scriptures, we are told to be equally yoked with fellow believers. (2 Corinthians 6:14) It is important that both the man and the woman are believers in Jesus Christ and that any marriage is centered around devotion to Jesus Christ. We noticed that you did not mention Jesus Christ, Jesus, Christ, God, or an abbreviation such as IJN (In Jesus' Name). Remember, "For there is one God, and one mediator between God and men, the man Christ Jesus," (1 Timothy 2:5) and "whoever will call on the name of the Lord will be saved.' " (Romans 10:13) It is only by the name of Jesus that we have access to God. Also, there is no other name by which we can be saved.
Now, regarding your nightmare, it is a reflection of the spiritual attack and the trauma you experienced. The Bible tells us, "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places." (Ephesians 6:12) Your dream is a manifestation of the spiritual warfare that is taking place.
Let us pray for you:
Dear Heavenly Father,
We come before You in the name of Jesus Christ, lifting up our sister who has been through a traumatic experience. We pray that You will heal her from the pain and trauma of the called-off wedding and the cohabitation outside of marriage. Forgive her Lord for any transgressions during this time. We also pray for the man involved that You would convict his heart and draw him closer to You.
We rebuke the enemy for attempting to attack her through nightmares. We ask, Lord, that You would surround her with Your hedge of protection and that You would command Your angels to guard her in all her ways. (Psalm 91:11)
We also pray for her future, that You would bring a godly husband into her life, a man who loves You and seeks to serve You. We pray that any future relationships would be centered around You and Your will.
In Jesus' name, we pray. Amen.
Be encouraged by this verse: "When you pass through the waters, I will be with you; and through the rivers, they will not overflow you. When you walk through the fire, you will not be burned, and flame will not scorch you. For I am Yahweh your God, the Holy One of Israel, your Savior." (Isaiah 43:2-3a)
Remember, God is always with you, and He will never leave you nor forsake you. (Deuteronomy 31:6) He is your refuge and strength, a very present help in trouble. (Psalm 46:1) Trust Him to heal you and guide you into a future that honors Him.
Prayer Focus: God, Thank You. Thank You for loving me. 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, mind, soul, body, 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. 
