4 Bible Verses about Marriages, Believers With Unbelievers

Do not team up with unbelievers [i.e., in close relationships, such as marriage, etc.]. For what do righteousness and wickedness have in common? Or, what fellowship can light have with darkness? And what harmony can Christ have with Belial? [Note: "Belial" means "worthlessness" and was used for referring to the devil]. Or, what does a believer have in common with an unbeliever? And what agreement is there between a temple of God and idols? For we are a temple of the living God, just as God said [Lev. 26:12], "I will live in them and walk among them [i.e., among His people]; and I will be their God and they will be my people."

Do not be fooled; bad company ruins good moral behavior.

We [also] know that we are [children] of God and that the people of the whole world lie under [the control of] the evil one [i.e., Satan].

Do you not know that your [physical] bodies are parts of [the spiritual body of] Christ? So, shall I take away parts of Christ's [spiritual] body and join them to a prostitute's body? Certainly not! Or, do you not know that the person who is joined to a prostitute is one body [with her, physically]? For God says [Gen. 2:24], "The two will become one flesh" [i.e., united in such a close relationship as to practically constitute one body]. But the person who is joined to the Lord is one spirit [with Him]. [Note: Just as the person who has sex with someone enters a close physical union with that person, so the person who becomes a Christian enters a close spiritual union with Christ].read more.
Stay away from [any involvement in] sexual immorality. Every sin a person commits is outside [the realm] of his body; but the one who commits sexual immorality sins against his own body. [Note: Possibly this means that sex, because it requires the deepest and most complete commitment of human involvement, becomes a unique sin when its true purpose and expression are violated]. Or, do you not know that your [physical] body is a temple [i.e., sanctuary] for the Holy Spirit, who lives in you and who was given to you by God? You do not belong to yourselves, for you were bought [by God] for a price. So, honor God with your [physical] body.