There are things our world accepts which Scripture does not allow Christians to do. One of those is – stating it plainly- sex outside of marriage.
1 Corinthians 5 states-
5:1 It is actually reported that there is immorality among you, and of a kind that is not found even among pagans; for a man is living with his father’s wife. 2 And you are arrogant! Ought you not rather to mourn? Let him who has done this be removed from among you.
3 For though absent in body I am present in spirit, and as if present, I have already pronounced judgment 4 in the name of the Lord Jesus on the man who has done such a thing. When you are assembled, and my spirit is present, with the power of our Lord Jesus, 5 you are to deliver this man to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus.
6 Your boasting is not good. Do you not know that a little leaven leavens the whole lump? 7 Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our paschal lamb, has been sacrificed. 8 Let us, therefore, celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth.
9 I wrote to you in my letter not to associate with immoral men; 10 not at all meaning the immoral of this world, or the greedy and robbers, or idolaters, since then you would need to go out of the world.11 But rather I wrote to you not to associate with any one who bears the name of brother if he is guilty of immorality or greed, or is an idolater, reviler, drunkard, or robber—not even to eat with such a one. 12 For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge? 13 God judges those outside. “Drive out the wicked person from among you.”
Living with someone before marriage or having relations with someone is evidence not of Christian faith but rebellion against God. It can’t be prettied up no matter how hard people may try. It is sin. The wages of sin- death.
Even if the whole world applauds immorality, Christians ought never.