Although the Old Testament lacks our modern terminology for sex, and tends to put a lot of time in on topics that we now take for granted (for example, even the most liberal of Christian tendencies still does not acknowledge bestiality), one really cannot say that the OT leaves the door open to premarital sex.
Here’s an example:
"If a man meets a virgin who is not betrothed, and seizes her and lies with her, and they are found, then the man who lay with her shall give to the father of the young woman fifty shekels of silver, and she shall be his wife, because he has violated her; he may not put her away all his days.” (Deuteronomy 22: 28-29)
No, God does not directly say ‘premarital sex,’ but commands that premarital sex must result in a marriage, and one that cannot be divorced from! Had she been ‘betrothed,’ the punishment would have been death for him and for her, except in the case of rape.
To understand the Divine attitude towards sexual contact with more than one partner, we must look to God’s commands regarding the Levites:
“They (the Levitical priests) shall not marry a harlot or a woman who has been defiled; neither shall they marry a woman divorced from her husband; for the priest is holy to his God. You shall consecrate him, for he offers the bread of your God; he shall be holy to you; for I the LORD, who sanctify you, am holy. And the daughter of any priest, if she profanes herself by playing the harlot, profanes her father; she shall be burned with fire.
“And he shall take a wife in her virginity. A widow, or one divorced, or a woman who has been defiled, or a harlot, these he shall not marry; but he shall take to wife a virgin of his own people, that he may not profane his children among his people; for I am the LORD who sanctify him." (Leviticus 21: 7-15)
Here, we are looking for a definition of the term ‘defiled’ which is not otherwise described. It is juxtaposed to ‘virgin’ and lumped in with divorcees, widows and harlots. Since only a virgin is a virgin, then a defiled woman is a ‘not-virgin,’ which thus assumes that she has had sex, unless you are willing to tamper with the definition of virginity, in which case we simply can’t have a discussion on the matter at all because words don’t mean anything.
The commands for the Levitical priesthood are not binding on Israel, but they are indicative of Divine view of sex. Premarital sex is ‘defiling.’ The woman is defiled and the man is a defiler, not a desirable state for either one, since both will have to answer to God for the defiling of His Image.
This leaves us with the question of why the topic of ‘premarital sex’ is not spoken of in a direct manner. The answer is cultural: those societies understood the importance of sexual continence before marriage. That’s why societies with looser sexual restrictions tend to not have prostitutes, since they are unnecessary if sex is easy to get. Even societies with relatively loose rules regarding prostitution still regard sexual conduct before marriage as undesirable. In fact, prostitution is generally seen as a form of either slavery or purposeful defiling, even if permitted.
Premarital sex is not a happy subject, because sex is not a happy subject. Even now when we have very loose standards, I doubt one could prove that people are any happier. Divorces, and unpleasant ones at that, are all too common. People are gulping anti-depressants and addicted to ‘drugs’ (including non-drug ‘drugs’ such as food, gambling, etc.) at an alarming rate. Western countries have shut down reproduction with the dissolution of the family, where children become an ‘option’ like whether or not to buy a Jacuzzi.
Student dorms and night clubs are full of lots of opportunity for one to express one’s sexuality, but they rarely produce long-term happiness and security. In the end, you can mess around a lot and still end up very lonely, which leads to more temporary relationships and more despair. Studies prove that ‘sexual compatibility,’ living together before marriage, open relationships, etc. do nothing but increase one’s opportunities for one’s unhappiness.
Sex is powerful stuff, and only a Divinely-inspired marriage is equipped to handle it. It is a sad day indeed when the Church would abandon it.