We are commanded not to fornicate (1 Corinthians 6:18) nor have inordinate affection and uncleanness (Colossians 3:5).
Fornication is considered sex outside of marriage, while adultery is considered sex with another who is not your spouse while in the covenant of marriage.
Fornication is a serious matter, considering it's the only legitimate reason Christ gave for divorce (Matthew 5:32, Matthew 19:9). I'm not sure which is considered the "bigger sin" by God (either fornication or adultery), but both are sins nonetheless according to the Bible and you should refrain from them, otherwise you will receive recompense from God for your sins. Just a friendly warning.
The most foolish thing a person can do is try to justify their sin by saying God's word doesn't "specifically" address what they're doing. The very fact you made a forum post about this for clarification proves that your conscience is telling you that you would indeed be sinning by having pre-marital sex. If you deny the Bible says not to fornicate, you are doing two things: 1). You are calling God a liar because it clearly says not to fornicate; 2). You are pridefully resisting the law of God.
You won't become unsaved (if you're saved already) on this matter, but God will punish you more because you knew it wasn't right and still pridefully acted out against him, trying to justify his own words for your actions. Woe unto you, friend, if this is the case.
Also, Paul clearly taught that if a brother is a fornicator, then we should have nothing to do with him, and we should shame him; we should put that wicked person away from us, and not associate with him, not even to eat with (1 Corinthians 5:11). So, take a hint that fornication is a pretty bad thing, friend.