A believer who is trying to justify getting married to an unbeliever is certainly asking for big trouble. Being in love blindsights people to practical eventualities. People make such marriage decisions with their heads in the clouds, and wind up losing head and heart. Being in love is not the agape of God. The eyes of romance either justify or refuse to see interferences that will become anything from nuisances to spirit-draining tragic griefs. Believers may believe that their love will overcome to bring the object of their affection to Christ, but it ain't so. If a potential spouse won't give themselves to the Lord before marriage, then the giant odds are that after marriage will take the believer's life in Christ and turn it into a life of confusion -- a real unequal yoke.
There is one place in Scripture where Paul addresses Christians who are already married to unbelievers, but he states that it is his own advice. For the most part, he is likely referring to former unbelieving couples where one spouse accepted the Lord.
1 Corinthians 7:
12 But to the rest I, not the Lord, say: If any brother has a wife who does not believe, and she is willing to live with him, let him not divorce her.
13*And a woman who has a husband who does not believe, if he is willing to live with her, let her not divorce him.
14*For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy.
15*But if the unbeliever departs, let him depart; a brother or a sister is not under bondage in such cases. But God has called us to peace.
16*For how do you know, O wife, whether you will save your husband? Or how do you know, O husband, whether you will save your wife?