Yes i am praying for your fiance to develop a strong faith in God. Faith comes by hearing and believing in the word of God. When we do this we have saving faith..for without faith it is impossible to please God Heb. 11:6. Faith is the channel through which Gods grace flows. Therefore without faith in God it is not possible to be saved. I pray he will come to repentance and be born again. The born again experience will completely change his heart and his life. He will not only believe in the word of God but he will love to read it and obey it. Once one has that initial small seed of faith to step forward and accept Christ as his savior through repentance he then will be able to perceive the awesome transforming power of God and he will never be the same again. He will have saving faith in God and be pardoned of his sins, doubts and misconceptions.
The Bible warns believers not to marry unbelievers (1 Cor. 6:14). If he does not come to saving faith in God I do not believe it would be God's will for you to marry him. I think it would be most wise to marry only another believer like yourself.
Dear heavenly Father i pray that this man who needs saving faith in you would come to know you in a personal and powerful way. Grant to him every available opportunity to come to saving faith and that born again experience that powerfully transforms the heart and lives of your people, Jesus name, amen