Non-marital sex is not ideal, but that doesn't mean Judaism has nothing to say about it.
Judaism may need new categories of sexual relationships in order to adjust to the reality of sex outside marriage.
While the Torah does not forbid premarital sex, the rabbis of the talmudic era prohibited it--but one modern authority proposed a sanctioned form of exclusive sexual relationship outside of marriage.
Gender & Sexuality
The Torah doesn't explicitly outlaw sex before marriage, but it doesn't approve of it either.
A selection of statements from rabbis of various denominations.