The mentions of sex in the New Testament are mostly Paul telling Christian communities to straighten up and fly right, and probably should not be generalised. The important points are made on the Old Testament books of Exodus, Leviticus and Deuteronomy.

The goal of the Bible, like in all adaptive cultures, was to create an environment of stable marriages where children could be properly raised, where men would know children were their children and thereby be incentivized to provide them with resources and where men could trust each other without worrying about being cuckolded. Anything that challenged that state of affairs was forbidden.

Hence the ideal was that females would marry young as virgins. Seducing or raping a virgin was bad, with the man having to compensate the girl’s father for diminishing her value as a wife and offer to marry her. Adultery, defined as sex between a married woman and a man other than her husband, was a capital offence. Female prostitution was allowed, and this reduced the temptation for men to commit adultery or seduce normal females.

Monogamy was the rule, although it was permissible for a man to take additional wives in some circumstances, which makes sense when there is a shortage of men due to wars and accidents. It is possible that the verses in Leviticus generally thought to prohibit male homosexuality actually prohibit polyamory.