It's important to note that the context of the verse in question has nothing to do with marriage. Rather, it is about not joining with unbelievers in their idolatry.
2Co 6:14 Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?
2Co 6:15 What accord has Christ with Belial? Or what portion does a believer share with an unbeliever?
2Co 6:16 What agreement has the temple of God with idols? For we are the temple of the living God; as God said, "I will make my dwelling among them and walk among them, and I will be their God, and they shall be my people. (ESV)