What is the ruling of Islam on a Muslim man marrying a Christian woman with whom he had an illicit relationship before marriage, and does this affect the unborn child?

You must engage in sincere repentance, frequent seeking of forgiveness, and righteous deeds for what you have done. Your marriage to the woman is valid, and your children are legitimate, provided that the woman has abandoned her ugly deeds and you are secure from her future betrayal.

There are fundamental differences between Muslims and Christians, including: - Christians believe in the Trinity, while Muslims believe in the Oneness of God. - Christians believe that Jesus is the Son of God, while Muslims believe that he is a servant and Messenger of God. - Christians do not believe in the message of Muhammad, peace be upon him, while Muslims believe that he is the Seal of the Prophets and the abrogator of previous laws. Allah says: "And We have not sent you except comprehensively to mankind as a bringer of good tidings and a warner. But most of the people do not know." (Qur’an 34:28) And Allah says: "And whoever desires a religion other than Islam, it will never be accepted from him, and in the Hereafter he will be among the losers." (Qur’an 3:85)

Your children are Muslims by birth, and you must raise them in Islam and teach them its laws. You must be wary of their mother drawing them or you to her religion.