Do not marry unbelieving women, until they believe: A slave woman who believes is better than an unbelieving woman, even though she allures you. Nor marry (your girls) to unbelievers until they believe: a male slave who believes is better than an unbeliever, even though he allures you. Unbelievers do beckon you to the Fire. But Allah beckons by His Grace to the Garden and forgiveness, and makes His Signs clear to mankind: That they may celebrate His praise. (Qur’an 2:221)
This law appears to be asymmetrical with respect to the leave for men to marry women of the book:
This day are all things good and pure made lawful to you…. Lawful to you in marriage are not only chaste women who are believers, but chaste women among the People of the Book, revealed before your time, when you give them their due dowers, and desire chastity not lewdness. If any one rejects faith, fruitless is his work, and in the Hereafter he will be in the ranks of those who have lost (Qur’an 5:5).
No mention is made of chaste “men” among the People of the Book, so only verse (2:221) appears to hold.
Of course, it depends on what you understand as “believer”: if we took believer to mean anyone who believes in the unity of God, for example, then there would be believers amongst the People of the Book, available to for the women.
But I prefer the asymmetry between 5:5 and 2:221. Because a woman is a field, a scripture, a space of signs, a pleasure of form. I mean this at all levels, at all her depths, across all her seasons, across her entire body. And a male is interpretation, seeding and reaping, projection, gaze: again, at all levels of his being, he is nothing more than an eye that surveys and reads her. So 2:221 dictates that multiplicitous licentiousness of masculine interpretation is not compatible with a divine scripture, a holy space of signs, a tawhid of form. And vice versa: an illuminated gaze and projection will not be compatible with a prostituted form.
Importantly, in the verse, the righteous woman is a single book, a single scripture, a single Qur’an. She cannot be inconsistent, her beauty derives from the consistency, the poetry of her single form. (The multiplicitous gaze of Samael/Iblisian is also denied for her, because it is, after all, the gaze of illusion. It might be more correct to say, denied by her very existence, in the sense that Shariah is a physical law — like the law of gravity — between what is Real and what is Illusory: he simply cannot locate her. Nevertheless, one can attempt to violate this law, with the dangerous repercussions of entering into illusion and, in a way, “being” beheld captive by that satanic gaze.)
On the other hand, 5:5 specifically concerns the masculine gaze in relation to forms of scripture: precursory forms of scripture, of the Book. This gaze may legitimately — and necessarily, in fact — extend from precursory revelations and fields, “what was revealed before our time”, into successive revelations and fields, what is to be revealed now. The righteous masculine gaze is a single interpretation, a single approach to seeding and reaping, running across the Feminine spaces of farmland, precursory to successive: here the masculine is invariant Truth of engendering.
The apparent asymmetry in fact prescribes a symmetry of the psyche’s gendered facets: the righteous woman is a single book, while the righteous male possesses a gaze, an illuminated interpretation that runs across, systematically, the transmission of Light between books, between the orbs of predication, between movement of the houses. His righteous gaze is invariant and hence singular in symmetry with the consistent singularity (Sakina) of the female-as-scripture (though from his perspective she may be manifold in temporality).
The verses concern the nature of masculine approach to interpretation/reaping in relation to the feminine fields, as they are constituted in temporal, poetic unfolding (books begetting/predicating over books).
In terms of practical marriage advice: if he is the right guy (that is, if he understands the truth of what I have written), go for it, whether he is culturally Muslim or not is 100% unimportant. What is important, and truly Muslim, is to physically grasp and act upon the nature of the righteous masculine interpretation demanded of your scripture/wife.