What if a woman has had oral sex with her boyfriend? Can she just repent and be forgiven? The Old Testament seems very harsh concerning death for them both. Why did God forbid it? I never had any blood when I first had sex. I was supposed to be a virgin up until the first time. How could a cloth in the Old Testament with blood on it be required for proof of virginity if some woman never bled when the hymen is broken?
Does God require you to marry if you have had sex?
Any sin can be forgiven if the person truly repents -- that is, changes his mind regarding his actions and starts working toward living as God asks. Unfortunately I find many who want the forgiveness without making any effort in changing their behavior. Perhaps the best definition of repentance is found in II Corinthians 7:11, "For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter." When people approach repentance in this manner, then God offers forgiveness for their sins.
You have a misunderstanding regarding the Old Testament laws, which is why you conclude they are harsh. The Old Law recognized three states in a person's marital life: unmarried, engaged, and married. The laws regarding punishment for sexual sins varied based on those states:
Married: To have sex with someone who was not your spouse was considered adultery. Not only was sex taking place outside of a marriage bond, but at least one person was also breaking the covenant they had made with their spouse. The punishment for this was death for both married person and the one whom he or she was having sex (Deuteronomy 22:22).
Engaged: Engagement was taken much more seriously in the past than we do today. When two people were engaged, a covenant was made between the two which was required to be honored. The two were almost equal to a married couple, other than they had not moved in with each other and had not yet had sex.
If an engaged woman has sex with a man and evidence shows it was consensual, then the punishment is the same as for adultery -- death. If there is a lack of evidence that it was consensual, then the woman is assumed to be innocent. The man was put to death for rape, but no consequence was given to the woman (Deuteronomy 22:23-27).
Unmarried: If an unmarried woman has sex, her partner was required to pay the normal dowry price as if he was going to marry her. In addition, he was required to marry her, unless her father objected (Exodus 22:16-17), and he gave up all rights to ever divorcing her (Deuteronomy 22:28-29).
The business about the proof of virginity has to do with honesty in dealings. You have to understand that in biblical days, as many cultures still do today, it was the parents who arranged a marriage. Sometimes a young man never met his bride until their engagement. The question is how to handle a deceptive agreement. What if a man was led to believe he was marrying a virgin woman but she wasn't? For a man to marry a virgin, he was required to pay the father a significant sum of money for the privilege of marrying her and he would have not way of knowing if the agreement was honest until after the marriage was sealed in a covenant.
"If any man takes a wife, and goes in to her, and detests her, and charges her with shameful conduct, and brings a bad name on her, and says, 'I took this woman, and when I came to her I found she was not a virgin,' then the father and mother of the young woman shall take and bring out the evidence of the young woman's virginity to the elders of the city at the gate. And the young woman's father shall say to the elders, 'I gave my daughter to this man as wife, and he detests her. 'Now he has charged her with shameful conduct, saying, "I found your daughter was not a virgin," and yet these are the evidences of my daughter's virginity.' And they shall spread the cloth before the elders of the city. Then the elders of that city shall take that man and punish him; and they shall fine him one hundred shekels of silver and give them to the father of the young woman, because he has brought a bad name on a virgin of Israel. And she shall be his wife; he cannot divorce her all his days. But if the thing is true, and evidences of virginity are not found for the young woman, then they shall bring out the young woman to the door of her father's house, and the men of her city shall stone her to death with stones, because she has done a disgraceful thing in Israel, to play the harlot in her father's house. So you shall put away the evil from among you" (Deuteronomy 22:13-21).
Notice that the proof of virginity was a protection for the woman against a husband who was mistreating her. It was not for the husband so he could get out of his marriage. It is easy to imagine cases where a man starts to hate his wife and goes around saying all sorts of malicious things about her, such as she was a prostitute before they married. Her parents could then present evidence of her virginity -- the blood spilled when her hymen broke as proof. Read the account again carefully and notice that it speaks of the evidences (plural) of virginity. The cloth would be one piece of evidence but not necessarily the only one. The cloth would be a significant one because we are trying to prove what didn't happen, which is a more difficult proposition.
If the evidence shows her to have been a virgin at her marriage, then the husband is fined double the dowry price that he already paid and the money goes to the parents who were charged with protecting their daughter's reputation. In addition, he forgoes any right to ever divorce his wife.
If evidence is found that she was not a virgin, then she was stoned to death for harlotry. What is overlooked is that under the Old Law, a death penalty could not be carried out unless there were at least two or three witnesses. "Whoever is deserving of death shall be put to death on the testimony of two or three witnesses; he shall not be put to death on the testimony of one witness" (Deuteronomy 17:6). The lack of blood on a cloth would only be one witness. The lack, but itself, would not be sufficient to trigger the death penalty.
What is not covered in this law is: 1) What happens when there is insufficient evidence to prove she wasn't a virgin and 2) what happens if a man knowingly marries a woman who is not a virgin.
So what happens in those cases where a woman is a virgin, but doesn't bleed on her wedding night? She would still have other sources of proof: the testimony of her midwife (doctor) when she was growing up and testimony of friends and family regarding her reputation. Also, consider that in cases where the parents are uncertain or lack proof of their daughter's virginity, they had the choice of not bringing the case to court. Then, if the husband wanted out of his marriage, he would have to gather evidence to prove a divorce case and even if he succeeded, the only consequence to the woman is that she is divorced. The death penalty only came when a woman tried to prove her innocence and was proven to have basically lied in court.