My sister doesn't want to get married because of statistics. She thinks that she'll have sex when she feels compatible with the person and when the prove they are loyal. But my thing is if you had that why wouldn't you get married anyways. Or wait to get married to that person when your lives are ready for marriage, or your ready to have a child. How would you not wanna confess your love to God your family and promise your commitment as in terms of forever and then have sex.
In modern relationships, marriage (in the most legal sense of the word) is often obsolete, and even damaging, considering the strains it puts on people financially, and the carnage legal divorces cause. And the ritual of marriage, at least in the oldest Abrahamic tradition, is about ownership of a woman, not about love. It's about paying a dowry to a woman's father to prove you can provide for her, to 'buy' her from the father and own her as property.
And even if many will say 'but it's not about that, it's not anymore, it's about love', well then love itself should be bond enough, if it's genuinely love.
There is no requirement for a couple to undergo a legal ceremony, or even a church ceremony, for a couple to be considered biblically married, and in fact, consummation is confirmation of a partnership to a greater extent than a church ceremony is. It is a commitment, by two people toward one another and toward the Godly way of sexual partnership, that is; faithfulness, compassion, patience, kindness, loving temperament, self-sacrifice, charity, forgiveness and benevolence.
Those are the real commitments, and the real tenets.
Outside of that, the bible doesn't actually forbid sex outside marriage, but it warns about uncontrollable lusts of all kinds, about allowing yourself to become bitter or 'hard-hearted', and about responsibility.