Praise be to Allah.
This problem – and many others – confirm the truth of what many daa’iyahs and reformers are saying about the necessity of being careful about how our sons and daughters are using the internet, and to beware of entering conversations between men and women in chat rooms, because of the very real fitnah (temptation] to which that may lead, with subsequent contact and meetings.
Undoubtedly your son made a mistake by forming this relationship with a non-mahram woman who is not permissible for him. He made a mistake by lying to you and by discussing this matter with his aunt. But we do not agree with the idea of refusing his marriage to this girl, especially if you think that your son is deeply attached to her. That is for the following reasons:
1 – Not every girl who acts in this manner can be judged to be deviant, badly brought up or of bad manners and attitude. This may have been a mistake on her part, as in the case of your son.
2 – What is happening to your son now, with his wanting to be alone and his falling behind in his studies may be because of intense love for this girl on his part. In such cases it may be that the only efficient remedy is for him to marry the one whom he loves. According to a hadeeth narrated by Ibn Maajah (1847), “There is nothing better for two who love one another than marriage.” (This hadeeth was classed as saheeh by al-Albaani in Saheeh Sunan Ibn Maajah).
3 – The fact that your son does not know much about the attitude and character of this girl may be dealt with by asking about her and finding out more about her background.
Hence we think that you should hasten to find out about this girl and her family. If her character is not good, then this will convince your son to stop thinking about her.
But if, after thoroughly investigating the matter, you like what you find out about her and her family, then there is no reason why your son should not marry her, rather this will be the best remedy for him and for her.
This suggestion applies if you feel that he is strongly attached to her and is keen to marry her, as referred to above. But if it is simply the matter of an idea that has occurred to him, and it is not the matter of love or deep attachment, and you hope that he will forget about her, then be firm in your refusal and help him to look for a woman who has good manners and is religiously committed and chaste. There are so many righteous and chaste women who have never had anything to do with men and have never faced temptation.
Turn to Allaah and ask Him to guide you, and seek His help by praying Istikhaarah concerning all the matters in which you want to take a decision.
And Allaah knows best.