We understand that you're considering a significant change in your life and seeking God's guidance and reassurance in this process. Firstly, we need to address a few things according to what the Bible teaches.
You mentioned moving in with your boyfriend. In the Bible, it is clear that sexual intimacy and cohabitation should only occur within the context of marriage between a man and a woman. Here's what the Bible says in First Thessalonians 4:3-5 WEB: "For this is the will of God: your sanctification, that you abstain from sexual immorality, that each one of you know how to possess himself of his own vessel in sanctification and honor, not in the passion of lust, even as the Gentiles who don't know God."
Living together before marriage is considered fornication. Fornication is sexual immorality which is sin, and this is against God's will for our lives. We encourage you to reconsider this path. Moving in together is not the same as marriage. Marriage is a specific commitment with specific rules outlined in the Bible. We should only have marital relationships within a marriage. Anything else is a sin.
Regarding your trust issues and insecurities, we encourage you to seek God's will and put your trust in Him, rather than in man. Psalm 56:3-4 WEB says, "What time I am afraid, I will put my trust in you. In God, I will praise his word. In God, I have put my trust. I will not be afraid. What can flesh do to me?"
In the context of a relationship that is not a marriage, you should not have these trust issues because you are not being put in a position to trust him. You are not in a position where you can be betrayed as a wife can be. However, in a relationship that is not a marriage, you should not have a position of trust over you like a wife would. You should be seeking to be married to a Christian Believer.
If you are not married, then you are not in a relationship where you have to trust him. You are not in a position where you can be betrayed as a wife can be. However, you should be seeking to be married to a Christian Believer.
Let's pray together:
Dear Heavenly Father,
We come before you today to lift up this dear sister in Christ. We pray that you guide her path and give her the wisdom to make decisions that align with your will. We ask that she trusts in Jesus Christ as her Savior. Help her to trust in you. We pray that her insecurities be replaced with the confidence that comes from knowing you and abiding in the Word of God.
We pray for the man in her life. We pray that if he is not a believer that he would be saved. If he is not ready to be married, then we pray that she would not be with him. Help them both to become believers and to do your will. We pray that the decision she makes would be to do your will and follow your commands.
Please forgive her if she has sinned. We pray that she would not sin but would walk in the Spirit. We pray in Jesus' name. Amen.
Remember that God loves you and wants the best for you. Trust in Him, and He will direct your paths according to His will. We encourage you to seek God's word and surround yourself with a community of believers who can support and encourage you in your journey.
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. 
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