How can one deal with a non-Muslim's desire to convert to Islam for marriage, along with fears that his intention may not be sincere, potential family opposition due to his ethnic background, and concerns about his later apostasy from Islam?

It is not permissible for a Muslim to love a disbeliever, for Allah Almighty says: ﴿You will not find a people who believe in Allah and the Last Day loving those who oppose Allah and His Messenger﴾. And whoever loves a disbeliever must abandon this love for the sake of Allah.

If a disbelieving young man declares his Islam, it is necessary to verify his sincerity by testing him, by asking him about Allah, His religion, and His Prophet Muhammad (peace be upon him), and about the religion he abandoned. This is also verified through his persistence in obligatory acts of worship such as prayer and fasting, his eagerness to inquire about lawful and unlawful rulings, his change of state by abandoning the rituals of disbelief and evil deeds, and his hatred for disbelief. This is based on the saying of the Prophet (peace be upon him): "There are three qualities, whoever has them will taste the sweetness of faith... and who hates to return to disbelief after Allah has saved him from it, just as he hates to be thrown into the Fire."

While emphasizing that no forbidden relationship should be established, as it is not permissible for a Muslim woman to touch or be in seclusion with a non-mahram man.