Ustadha Raidah Shah Idil makes it clear that a Muslim woman cannot marry a Christian man.
If a Muslim woman wants to marry a Christian man on the condition that he will allow their children to be practicing Muslims, and their life and all matters will be handled as per Islamic teaching, then is there an issue in getting married?
The Qur’an doesn’t mention clearly that Muslim women are prohibited from marrying Christian men. It seems to be just a matter of scholars thoughts or considerations.
“Do not marry polytheistic women until they believe; for a believing slave-woman is better than a free polytheist, even though she may look pleasant to you. And do not marry your women to polytheistic men until they believe, for a believing slave-man is better than a free polytheist, even though he may look pleasant to you. They invite you to the Fire while Allah invites you to Paradise and forgiveness by His grace. He makes His revelations clear to the people so perhaps they will be mindful.” (Sura al-Baqara 2:221)
Dear sister, it is not permissible for you to marry a Christian man.
There is no scholarly difference on this very clear matter. Please refer to these previous answers for further clarification: Can a Muslim Woman Marry a Non-Muslim Man if Their Children Are Raised as Muslims? and Why Is a Muslim Woman Not Allowed to Marry a Non-Muslim Man?
The only way for your relationship to be made halal is this – he must embrace Islam, and you must do a valid nikah with him.
Your marriage contract to a non-Muslim man is invalid, causing your children to be born out of wedlock. Your unborn children will be innocent of your sin of zina, but they deserve a better start to life. Please read: Can I Claim a Child from an Illicit Relationship?
Reality of Your Situation
You are both already in love, want to marry, live by Islam and raise your children as Muslims. As a courtesy to you, your Muslim family, his own soul, and most of all, to Allah Most High, please encourage your partner to embrace Islam.
Even if he does not fast a single day in his life or complete a single prayer, it is better for him to die on belief, so the Prophet, peace and blessings be upon him, can intercede for him on the Day of Judgement. Death, Hellfire and Heaven are real. Would you not want the man you love to be with you and your children in Paradise?
I encourage you to share this with your partner: Advice to a Christian Man Who Wants to Marry a Muslim Woman.
I pray that Allah opens his heart to Islam, and blesses you with a loving marriage and pious children.