In this case, if you are a Christian and the man is not a Christian, then the Bible is very clear that you should not marry him. In fact, I normally counsel people of faith not to even date or court with unbelievers, so that they do not fall in love with them and have to break off a relationship (studies show that you will usually marry someone you've dated …). The principle passage for this is 2 Corinthians 6:14-18, which says,

6:14 Do not become partners with those who do not believe, for what partnership is there between righteousness and lawlessness, or what fellowship does light have with darkness? 6:15 And what agreement does Christ have with Beliar? Or what does a believer share in common with an unbeliever? 6:16 And what mutual agreement does the temple of God have with idols? For we are the temple of the living God, just as God said, “I will live in them and will walk among them, and I will be their God, and they will be my people.” 6:17 Therefore “come out from their midst, and be separate,” says the Lord, “and touch no unclean thing, and I will welcome you, 6:18 and I will be a father to you, and you will be my sons and daughters,” says the All-Powerful Lord.

I'm sorry to deliver this bad news, but I suspect you knew all along that marrying this person would not honor God. I pray you will make the right decision.