1 Corinthians 6:9-11

9 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,

10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.

11 And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.
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Adulterer - Voluntary sexual intercourse between a married person and a partner other than the lawful spouse

Fornication - Sexual intercourse between partners who are not married to each other


Seems to me with there being two different mentions of sexual relation outside of marriage potentially keeping one out of Heaven I would suggest keeping it zipped up till there's a ring on that finger.