If we get married, will the sin stop?

Answer:

Yes, there is a real person here who really answers questions as his time allows.

Critical information is missing, making it difficult to answer your question. From the way you worded it, I assume you have not been married before.

Basically, God allows one marriage for a man and woman, and that marriage is expected to last a lifetime. "And He answered and said, "Have you not read that He who created them from the beginning made them male and female, and said, 'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh'? So they are no longer two, but one flesh. What therefore God has joined together, let no man separate" (Matthew 19:4-6). Death of a spouse allows the living spouse to marry again. "For the married woman is bound by law to her husband while he is living; but if her husband dies, she is released from the law concerning the husband" (Romans 7:2). A second allowance is when a person divorces his spouse because was having sex with other people. "And I say to you, whoever divorces his wife, except for immorality, and marries another woman commits adultery" (Matthew 19:9). The spouse who was not involved in adultery is allowed to remarry after the divorce. However, the spouse guilty of adultery is not allowed to remarry. The guilty spouse remains bound by his or her covenant until the original spouse dies.

Thus, if the woman you are living with divorced her husband because he was cheating on her, then she can marry you. If the divorce was for other reasons, she cannot marry until her original husband dies.

Regardless, what you and she are involved in is fornication. You are having sex without marriage, which is against the teachings of God. "Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God" (I Corinthians 6:9-10). You cannot gain forgiveness of sin until you stop the sin and stop thinking that the sin is acceptable (II Corinthians 7:10-11). Moving out until you get married is one way to stop the sin. Getting married tomorrow (assuming she has the right to a second marriage) is another way to stop the sin.

If the woman you are living with doesn't have a right to a second marriage, then your sex with her is adultery because she remains bound by her covenant with her first husband. Even if you marry her, it remains adultery (Romans 7:3).