If two people love each other can they live together and have sex?

The Bible teaches sex is only to be within the confines of marriage where a man and a woman are committed to each other for life. Otherwise it is called fornication. The Bible takes this seriously, because God performed the first marriage when there was only one man and woman alive and blessed them telling them to be fruitful and multiply.

Galatians 5:19-21: “Now the works of the flesh are evident, which are: adultery, fornication , uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies,  envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God.

Ephesians 5:3-4: “But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints;  neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting,

Colossians 3:5-8 “Therefore put to death your members which are on the earth: fornication , uncleanness, passion, evil desire, and covetousness, which is idolatry. Because of these things the wrath of God is coming upon the sons of disobedience, in which you yourselves once walked when you lived in them.”

If you are a Christian you are not to be living together having sex outside marriage. God tells us to do things the way He commands for our protection. God honors those who keep his ways

Hebrews 13:3-4 “Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge.”