My ex-boyfriend and I committed fornication. We both knew it was wrong to do what we were doing, but the feelings just got the best of us. We both understand now that we have committed a very grievous sin against God. I have really struggled with the guilt and pray every night and morning for God to forgive me. I am just very worried about being able to get married later on in life. Not only have I made a very big commitment to this ex-boyfriend, but I know it says that the only penance for fornication is marriage. He doesn't want anything to do with me. Does that mean I will never be able to get married?
The sin didn't just occur when you had sex, it had been present for quite a while as the two of you went
- from lust (a strong desire to do what is unlawful) "But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart" Matthew 5:28)
- to uncleanness (when you were talking dirty to each other) "But immorality or any impurity or greed must not even be named among you, as is proper among saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God" (Ephesians 5:3-5).
- to lewdness in the form of sexual touching "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1).
Things didn't get out of control when stripped down. It was out of control when you chose to go toward sin thinking you could stop if you wanted to. You didn't count on the fact that instinct takes over and you don't want to stop.
Now that this boy has gotten what he wanted from you, he's left; which shows you made another mistake in picking who you wanted as a boyfriend. Not only did he not honor you and protect you, he used you and dumped you. One of the reasons God said sex belongs only in marriage is because a guy has to first prove he is committed to you only in the wedding vows before he can have your body. Instead, you gave yourself away cheaply.
I don't know where you got the idea that you can only marry the person you first have sex with, but it wasn't from the Bible. Even the Old Testament did not have such a provision. It did say that a guy who who had sex with a girl had to pay a dowry as if he was marrying the girl and that he had to marry the girl, unless her father said no.
"If a man entices a virgin who is not betrothed, and lies with her, he shall surely pay the bride-price for her to be his wife. If her father utterly refuses to give her to him, he shall pay money according to the bride-price of virgins" (Exodus 22:16-17).
"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" (Deuteronomy 22:28-29).
But we don't live under that law today.
You sinned, but you can repent, which means change you attitude toward sex before marriage (not just the act of intercourse, but the whole chain sins that lead to it) and change your behavior. If you are not yet a Christian, it is past time to get your life right with God. See How to Become a Christian for more information. If you are a Christian, then you need to admit your sins and move on from there to living righteously. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9).
Finally, you need to learn how to pick a good man who will be a faithful husband to you. Sexual excitement is not the measure of a good man.