I was recently asked this question via a FaceBook chat. The “friend” who asked it was someone I did not personally know but who had visited the church. I anticipated after my answer they would sign-off with a quick “thanks” or less. I was pleasantly surprised. Here is what I told them: The Bible is very clear on that issue.
Answer:Typically “fornication” is the term used to refer to sex before marriage whereas “adultery” refers to sex after marriage with anyone other than your spouse. The Greek word the KJV translates “fornication” actually includes many forms of sexual immorality (incest, prostitution, harlotry, etc) and so is often simply translated “sexual immorality”, so as not to limit its meaning to fornication. The Bible is clear that sex before marriage, and all sexual immorality, is a sin and warns of harsh penalties for those involved in it.
The Bible teaches self-control and complete abstinence before marriage and a one-man, one-woman relationship after marriage both physically and in the area of the thought life.