I agree with yes2truth. I wish to add that from my studies I now believe that fornication in the biblical sense is idolatry, not sex before marriage.
I also don't think consensual sex among adults is fornication or adultery. Adultery, to me, involves a betrayal, such as a desire to leave the marriage for someone else. Fornication, to me, is idol worship. If sex is your idol then I guess that's fornication. But all normal healthy people like sex, so when does it become idolatry and who is to judge?
Abraham had sex with Hagar and it was approved by Abraham's wife Sarah, and who knows how many other maid servants he joined with for sex? David and Solomon had many wives and sex slaves as well.
I see a double standard preached where certain men of God in the OT were able to have hundreds of sex slaves...and NT preachers gloss over that and tell us we can't have any fun. So men end up frustrated and commit other sins, or even commit crimes, all because they don't get enough sex and can't control their natural passions. I see lying, cheating, stealing, murdering, arrogance, selfishness, gossiping, gluttony, being angry at people without a just cause, etc. as being more sinful than having consensual sex.
We are so hung up on sex as being evil that we miss the things I just mentioned above, and many people end up living lives plagued by guilt, hangups, and inhibitions.