We are saddened to hear about your brother's situation and we are here to intercede on his behalf to our Lord and Savior Jesus Christ.
Firstly, it is important to address your concern regarding the importance of Jesus. It is only through the name of Jesus Christ that we have access to the Father, and there is no other name by which we can be saved. As the Bible tells us, "For there is one God, and one mediator between God and men, Jesus Christ" and "in no other is there salvation, for neither is there any other name under heaven, that is given among men, by which we must be saved!" (Acts 4:12).
Your brother's relationship issue is something we need to discuss. The Bible is clear that God's design for intimacy is within the bounds of marriage between a man and a woman. "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous." (Hebrews 13:4). Any intimate relationship outside of marriage is considered fornication, which is sin.
Fighting and disagreements are normal in relationships, we all make mistakes and do things we later regret. Pray for wisdom and discernment for your brother to understand God's will for his life, for God to change her heart or move them both on. It is crucial to remember that God's will is for your brother to marry a woman of God who will support and encourage him in his faith.
Regarding his absence from fellowship, the Bible tells us not to forsake the assembling of ourselves together, as is the habit of some, but to keep encouraging one another, and all the more as you see the day approaching. (Hebrews 10:25).
Let us pray together:
Dear Heavenly Father,
We come before You today in the name of Jesus Christ to lift up our brother and sister who is in need of Your guidance and intervention. Lord, we ask that You soften his heart and fill him with Your Holy Spirit. Help him to see the error of his ways and turn back to You.
Lord, we pray for wisdom and discernment for him in his relationship. If it is Your will for them to be together, we pray that You would heal their relationship and guide them towards a godly marriage. If it is not Your will, we pray that You would give him the strength to walk away and trust in Your plan for his life.
We also pray that he would return to fellowship with other believers. Lord, convict his heart and draw him back to You. Help him to see the importance of surrounding himself with a community of believers who can support and encourage him in his faith.
Lord, we ask all these things in the name of Jesus Christ, our Lord, and Savior. Amen.
Be encouraged, for God is faithful and hears our prayers. Trust in His perfect will for your brother's life. Keep praying and interceding on his behalf, and remember that God's timing is perfect. Do not forget to praise God through all the trials and troubles.