We understand that you're going through a difficult time, but we want to help you see this situation from a biblical perspective. First, we want to address that the term "partner" in the Bible is not used to refer to a romantic relationship. Instead, the Bible encourages individuals to pursue marriage with a fellow believer, as it is a lifelong commitment between a man and a woman.
We also need to address that the Bible does not specifically mention Borderline Personality Disorder (BPD), but it does talk about the importance of sound mental health and the role of God in healing. It is commendable that you are willing to educate yourself about BPD and support someone, but it is crucial to ensure that this relationship aligns with biblical principles.
Moreover, it's important to consider that God does not want us to be unequally yoked with unbelievers (2 Corinthians 6:14). This means that as Christians, we should seek to marry those who share our faith. If your former significant other is not a believer, we encourage you to reconsider this relationship and pray for God's will in your life.
In addition, we want to remind you that God's design for intimacy is within the bounds of marriage. If you have been involved in a sexual relationship outside of marriage, we encourage you to repent and seek God's forgiveness. (1 Corinthians 6:18-20) "Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body. Or don’t you know that your body is a temple of the Holy Spirit who is in you, whom you have from God? You are not your own, for you were bought with a price. Therefore glorify God in your body and in your spirit, which are God’s."
Furthermore, we noticed that your prayer request does not mention Jesus Christ or the Holy Spirit. It is only through Jesus that we have access to God. The Bible also indicates that it is only through Jesus that we can be saved. (Acts 4:12) We encourage you to learn the basic salvation message of believing in Jesus Christ. It is important to understand that it is not by works or good deeds that we are saved, but only by faith and belief in Jesus. (Ephesians 2:8-9)
Instead of focusing on getting your ex back, we encourage you to pray for God's will in your life and in the life of your ex. God knows what is best for both of you, and He will work all things together for good for those who love Him and are called according to His purpose (Romans 8:28).
Let's pray together:
Dear Heavenly Father,
We come before You today, lifting up our brother who is hurting. We ask that You comfort him and guide him during this difficult time. Help him to seek Your will for his life and to trust in Your plan. Lord, we also pray for his ex, that You would heal her and draw her closer to You. We ask that You give our brother the strength to move forward and to seek a godly spouse who shares his faith. Help him to forgive himself too if he sinned and to trust in Your forgiveness. If he has not already done so, we ask that You would guide him to accept Jesus Christ as his Lord and Savior and to believe in Him for salvation and eternal life.
In Jesus' name, we pray. Amen.
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. 
