Does anyone know if it’s sinful to have sexual relations with a man if you are not a wife but a gf? ( in Old Testament)

So I’m studying the Old Testament only and that’s what I was trying to figure out in modern time.

I know men are able to have wife’s and concubines.

I know that “harlotry” is forbidden. Which is a modern day prostitute or promiscuous woman. -Leviticus 19:29 “Do not profane your daughter by making her a prostitute, lest the land fall into prostitution and the land become full of depravity.”

Wives are obviously acceptable but they must be virgins. -Leviticus 21:13-14 “And he shall take a wife in her virginity.

14 A widow, or a divorced woman, or profane, or an harlot, these shall he not take: but he shall take a virgin of his own people to wife”

What about concubines? “a woman with whom a man cohabits without being married”

If they were allowed in the Bible are they expected to be faithful to ONE man or not since they’re aren’t wives? I’m a little confused.