There is a great difference between a change of mind and a change of heart. A person’s mind can be shifted by a compelling argument, a powerful book, or even by a strong emotion. But the heart, the deep, inner seat of who a person really is, rarely changes. The heart changes only when it is born again, when it is given completely to the Lord. Until that happens, a change of mind is often just temporary. What is really in the heart will eventually come out again. You cannot change your heart by altering your actions or by simply adopting new ideas. Out of the heart flow the issues of life.
What you are longing for is more than a mere shift in his thinking. You are hoping for the kind of transformation that only the Spirit of God can accomplish. It is not up to you to argue him into believing rightly, nor is it up to you to convince him through reason alone. Only God can create a response in the heart. Your place is to witness to the truth in love, and then it is up to the Spirit of God to take that witness and do what He wills within that man’s heart. This is hard, because you love him and you want to be with him. But God’s Word is forever settled in heaven. It does not change with the mores of a society or the painful experiences of an individual. We are never entitled to challenge it or seek to reshape it. The things you recognized as wrong in those books, the larger theology that troubled you, those are serious matters. The truth does not bend to accommodate our past hurts or our cherished desires.
The difficult conversation you are preparing to have may feel like a wound. When you are open and honest, it can hurt. But faithful are the wounds of a friend. Though they hurt, they are intended to heal. Be careful that your own heart is right before the Lord in this. Do not speak from a place of frustration or merely to prove a point. Speak because you fear hurting the God who loves you. True fear of the Lord is not being afraid that God is waiting to harm you. It is a loving dread of doing anything that would break His heart. And it does break His heart when His children walk after the imagination of their own hearts instead of walking in His truth.
Do not let your heart be consumed with worry over his reaction. Pour out your grief before the Lord, but then let your heart muse over good things, things that touch the King. God loves your fellowship. Your prayers rise before Him. He knows the secrets of every heart, including yours and including your beloved’s. Trust the Lord to search it out and to do His work. Real peace will never come by simply hoping another person changes. Peace comes when you discover the grace of God and rest in His unchanging character. His love for you does not alter from one day to the next, regardless of how another person responds to His truth. Let His constant love steady you as you walk in obedience.