My Mother is non-Muslim. If she has a boyfriend and he moves into the house with us, I can never ever marry him because he's had sex with my mother, right? So, if I can never marry him, does that make him my Mahram? Do I have to wear Niqab in my house when he is there?
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If this man is Muslim, he should adhere completely to the obligations of the Sharee’ah. He should know that Zina (fornication or adultery) is a major sin, which he should immediately give up, repent from, feel deep sorrow for having committed it and have firm resolution not to repeat it in the future. On the other hand, this man is not your Mahram. So, you must adhere to Hijaab completely when you are at a place where he can see you. He is a non-Mahram (marriageable) man like any other non-Mahram men. Moreover, this man who committed Zina with your mother, is not forbidden to you in marriage. There is no objection in the Sharee’ah to his becoming your husband provided he repents and becomes a pious man. This is the most preponderant opinion among the scholars of Islam and it is the most correct one. But some scholars believe that it is forbidden that a man who has had illegal sex with a woman marries her daughter. Anyway, exhort your mother and try to convince her to stop committing this abominable sin and to become a good Muslim.
May Allah guide us all to the right path.
Allah knows best.
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