I'm not sure what your point is about concubines. And you're wrong about non-virgins being prohibited from ever marrying (e.g. Deut 24:1-4). But you're right about the penalty for adultery (i.e. lying with another's spouse):
Lev 20:10 "The man who commits adultery with another man’s wife, he who commits adultery with his neighbor’s wife, the adulterer and the adulteress, shall surely be put to death."
Deut 20:22 “If a man is found lying with a woman married to a husband, then both of them shall die — the man that lay with the woman, and the woman; so you shall put away the evil from Israel."
Sex outside of marriage when neither of the parties is married is also dealt with:
Deut 22:28-29 “If a man finds a young woman who is a virgin, who is not betrothed, and he seizes her and lies with her, and they are found out, then the man who lay with her shall give to the young woman’s father fifty shekels of silver, and she shall be his wife because he has humbled her; he shall not be permitted to divorce her all his days."
In the context, Deut 22:28-29 is about what happens when two people not married to each other are found to have slept together, whether or not it is consensual. For instance, the preceding verses excuses the woman in the case that she is found to have slept with a man if it was in the country, because she may have shouted without anyone hearing it: she is excused because of the possibility that it wasn't consensual and she did nothing wrong.
Thus the big picture is that sex implies marriage, and marriage implies sex. It was simply assumed that one did not exist without the other. In the example above, those who had sex must get married. Or Gen 24:67, "Isaac brought her into the tent of his mother Sarah, and he married Rebekah. So she became his wife." Or Deut 22:20-21, where if a newlywed bride is not a virgin, she is punished (cf. also Lev 21:9). Fornication, often called "whoredom" or "harlotry", is categorically forbidden (Lev 19:29).
I won't spend time here explaining how each of the laws I've mentioned are both wise and fair. Suffice it to say that it is unfair to criticize these laws as if they were superimposed upon the culture and society in which we live today.