Matthew 5:28
But I say to you, everyone who looks at a woman with an improper sexual desire for her [body], has already been sexually unfaithful to his mate in his heart.
1 Corinthians 6:9-11
Or, do you not know that evil people will not possess God's kingdom? Do not be misled: neither will sexually immoral people, nor idolaters, nor those who are sexually unfaithful to their mates, nor homosexual perverts. [Note: The Greek uses two words here, denoting both the passive and active partners in male homosexual acts].
1 Corinthians 10:20
[Certainly not!] But I am saying that the Gentile sacrifices are [really] offered to evil spirits and not to God. And I do not want you to have fellowship with evil spirits.
Galatians 5:19-21
Now those things done by the sinful, physical nature [of a person] are evident; they are these: sexual immorality, moral impurity, indecent conduct,
Hebrews 13:4
Marriage should be considered honorable among all people and its sexual responsibilities should be faithfully kept. For God will judge [and condemn] those people who are sexually immoral and who are sexually unfaithful to their mates.