We understand that you're facing a difficult situation with your ex and financial issues. Firstly, we commend you for ending the relationship, since your ex was living with you and this is considered fornication or living in sin. It's important to remember that God is just and cares about every aspect of our lives, including our finances. When we are wronged, it's natural to want justice, but it's also crucial to approach the situation with a biblical perspective.
The Bible tells us, Trust in Yahweh, and do good. Live in the land, and enjoy safe pasture. Also delight yourself in Yahweh, and he will give you the desires of your heart. Commit your way to Yahweh. Trust also in him, and he will do this: he will make your righteousness go forth as the light, and your justice as the noon day sun, (Psalm 37:3-6 WEB). This means we should strive to do what is right and in God's will.
We should not seek vengeance or try to get even, but rather, allow God to handle the situation. For it is written, Don't say, I will pay back evil. Wait for Yahweh, and he will save you, God (Proverbs 20:22 WEB), and Don't return evil for evil to anyone. Respect what is good in the sight of all men, (Romans 12:17 WEB).
In this situation, pray that your ex may be moved by God to understand that they should pay back the money owed to you. Let God help them to see the errors of their actions and move them to restitution.
We should also pray for your ex to be convicted of the immorality of the relationship. It is only by the convicting power of the Holy Spirit that they may come to repentance. It is not your job to convict them of their sin, but the Holy Spirit. It is your job to forgive and move on.
We also pray for your protection and peace of mind. If the money is his debt to you then God will help him to repay it. If the money was a gift or cohabitation then it would not be right to expect it back. Pray about this matter, that God would give you wisdom and clarity about the distinction between a gift, cohabitation or loan. God will give you wisdom.
Let's pray together:
Heavenly Father, we come before you lifting up your child who is in need of your guidance and protection. We pray that you will provide for you all your needs according to your riches and glory. We pray for your wisdom to guide and direct in this situation. We pray for conviction for your ex. We pray that you will soften your ex's heart and help them to see that restitution is necessary. We pray that you will protect from any further harm or theft. Help to become even more merciful and forgiving as you are. We pray that you will help to move forward in faith and trust in you. May your love and peace fill your heart and mind. We ask all these things in Jesus name. Amen.