This is a sensitive area. Looking at the Scriptures will help us to go into the right direction.
Warning against marrying an unbeliever
Marrying an unbeliever is warned against in the letter of Paul to the Corinthians: “Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?” (2 Corinthians 6:14). Although this verse was probably not particularly written with marriage in mind, it is most certainly relevant for marriage. Paul teaches us to keep ourselves pure from the idolatrous practices of the world. Yoking closely with an unbeliever will make it very hard for a believer to walk with God and not fall into temptation. We are taught to pray: “Lead us not into temptation” (Matthew 6:13), but by marrying an unbeliever you walk into it of your own accord. Marrying an unbeliever qualifies for being very closely yoked to an unbeliever. When you marry, you form a new unity: Genesis 2:24.
Placed into the kingdom of light
When you came to faith in Christ, you were taken out of the kingdom of darkness and placed into the kingdom of light (Colossians 1:13). So how could you then have fellowship with a person who’s still in the dominion of darkness? It will be impossible to share the most important part of your life with him or her: your spiritual relationship to Jesus. Also when you start having children, it will be hard to form a unity with your spouse when it concerns their spiritual upbringing.
Give him or her time to get to know the Gospel
When you start having a relationship with an unbeliever and it develops into a more intimate relationship, you could give him or her time to get to know the Gospel. In some countries it is very hard to find a husband or wife who is a Christian, because there are so few of them. In that case it is a good idea to have your fiance(e) meet with the pastor or an elder of your church and offer him or her the opportunity to study the person of Christ. Of course nobody can force him or her to convert to Christianity and there is a danger that he or she will become a ‘Christian’ because of you, but at heart remains a nonbeliever. Pray that the Holy Spirit will lead you in this matter and be prepared to trust and obey him.
Do you accept God’s word as authoritative?
The bottom line in matters like these is: Do you accept God’s word as authoritative, also when it concerns more sensitive issues in your life? Do you trust Him with all areas of your life? Allow Him to lead you onto his path and trust Him that his ways are best. Have a long look at the following passages: Proverbs 3:6-8; Psalm 32:8-11; Psalm 95:7-11. All these passages have this in common: Trust in God and you will find real joy.