Can you point me to the verse(s) that say sex outside of marriage is a sin ? I know there are verses that say adultery is a sin, but I'd like to see ones that say sex outside of marriage is sinful.

1 Corinthians 6:18, Galatians 5:19, 1 Thessalonians 4:3 and others depending on how you translate the greek "porneia". Historically it has been translated to mean various kinds of sexual immorality, including, but not limited to adultery, homosexual sex, bestiality, incest, prostitution, idolatry and generally sex with anyone other than your marriage partner. An honest treatment of the Bible's teachings on marriage and fidelity as well as a look of the culture of the time of Christ constrains me to believe that this would include premarital sex.