Home and Enclave
There are two ways of establishing a household with others: a home and an enclave. The latter is gender exclusive. The ideal form of this would be a monastery, and the perversion of this would be bad monasteries, such as the many college dormitories you see in America today in both secular and Christian colleges. These housing situations are founded on a lie: that it is good (or at least neutral) for men with different purposes and virtues, men from wildly different walks of life, to be arbitrarily thrown together in small, condensed spaces with no means of order, authority, or recourse. An RA is hardly an abbot. Dorm life is organized much more by profanity, squalor, doritos, and late night video game seshes than it is organized by prayer, fasting, and psalm-sing. The ability for home-making is reduced to the small artifacts with which a given man decorates his living space, all the way from pin-ups to branches decorated with Christmas lights. They are unable to provide any hospitality because they have no dominion or freedom. The ideal model for unmarried men, then, is to come together in enclaves built around shared vocation and ideals, so that they can help develop each other's skills and minds. They can create a space of welcome for travelers. The perverse form of this is a fraternity, where the shared ideal is, once again, base sensuality. The other way of living with another person is by home. This is not gender exclusive because you are able to bound to someone of the opposite sex by blood or by covenant. The bodies of men and women are not designed to live and work together day to day according to ideal purposes, at least in the same way that women and women can and that men and men can. Rather, they are designed to be joined bodily, either in the marital sense or the filial sense. But we know that it is perverse and pathetic for adult men to live only with their mothers and perhaps even for men to live only with their adult sisters. It is not that there need be any immoral relations between them; incest happens but it happens because of sin, not because of living arrangement.
An arrangement in such a fashion is not perverse because of incestuous paranoia but because it denies the reality of what men, women, and homes are suppose to be. The nature of a home is to be a place where a man has left his father and mother and is joined bodily with a woman. Their body together forms the living space for new life. The parents' body in the broad sense (that is, everywhere they have authority, within their house and on their land), nurtures the child after it has left the literal body. Then that child in turn comes of age and leaves to join an enclave or form a new home. Adult men who do not do this are often seen as infantile, for good reason: they have not left the 'body' of their mothers. Let us remember that mothers are not just home makers; they are a world and world makers: out of and around their body they bring abundant life. But this only comes about from the union of a husband and a wife: seed and field together make a farm. For a man to leave his father and mother is to leave an entire world, like leaving the earth itself, but it is necessary if he is going to make his own world. Groups of men or women caught in the In-Between Seasons of Being should form enclaves together with their kind; way-stations.
Some would say that an unmarried adult man and an unmarried adult woman can live together without immorality, without touching one another. Let us say they are great friends, have no sexual interest in each other, and need a roommate for a season. Now it is very possible that they could go through that season without any sexual interaction. Their life together would still be unhealthy, because they have denied what it means to live in a home and habit with another person. A group of men or a group of women may be organized in daily living by a shared code or ideal. A man and a woman may be organized in daily living by their shared bodies and shared covenant. But a man and a woman who live together who do not share blood, body, covenant, or code really cannot live healthfully at all. They are essentially both hermits, with the added challenge of living very close to an actual physical body by which to become tempted or at the very least confused. Their home will be a confused and impoverished one, because they have denied themselves the ability to be joined in any meaningful sense beyond friendship, and friendship is very different than a home.
Now, why can't a man and a woman share a code? Why can't we have co-ed monasteries? Besides the obvious practical impossibilities (that is to say, non-stop hanky-panky), from a purely theoretical level: could it happen? I would say not. A code of life has to be intentionally designed to the vocation of the people sharing that code. A man and a woman, on account of their separate bodily realities, have inherently different vocations. Even within a shared occupation, a man and a woman naturally express their vocation differently because of physical necessity.
Men and women are supposed to be joined bodily, either through shared blood or through the intimacy of marriage. I believe well enough that men and women can be good friends without any sexual immorality, because I have seen it. This is only natural: after all, we are all brothers and sisters in Christ. But the ways of friendship are distinct from the ways of daily home life. Even setting aside the temptation for immorality, I cannot imagine that living in closeness unbound day and night could be in any way healthy for one's friendship in any season. So there may or may not be sin in the end. But I do believe there will be a denial of nature and thus impoverishment.
Still, perhaps someone could offer a concrete example of a man and a woman living together in total virtue, perfect love, and a passionate engagement with the world, all without any of the bonds I believe are necessary for daily home life: vision, body, blood, covenant, code. If so, I would have to revise my understanding. But I can't imagine that ever being offered.