Nothing wrong with pre-martial Sex.
Pre-marital Sex is NOT fornication or sexually immoral.
Paul Defines fornication in the Bible as joining in with the pagan worship of a pagan fertility god per Paul Bible definition per 1 Cor 10:8 compare to Nu 25: 1-9 Nu 31
God is very pro-sex. God made sex and human sexuality and said it is excellent. Gen 1:31