It is not easy for us to understand the concept of Friendship as it existed in earlier Christian societies, because of presuppositions innate in our own society; a society which, compared with earlier societies, seems to me to be riddled with abnormalities.
The most obvious of these is the assumption that the only relationships that can exist between humans must necessarily be sexual or have strong sexual components. Thus people can even assume that the great love that existed between David and Jonathan must have been sexual. But, given the prescriptions in the Torah concerning homosexual actions, such an eisegesis is manifestly ludicrous. Quite apart from that, the other textual evidence concerning David and Jonathan is very far from suggesting that the tradition regarded them as 'homosexuals'. Their love 'surpassed that of women'; this means that it was not a physically transposed version of the sexual relationship of man and woman in which (except that anus is substituted for vagina) the physical and emotional modalities are closely parallel. It means that it was different in kind. In the Greek epic tradition, the great love between Achilles and Patroclus is contextualised by the information that, in the hut they shared, each slept with his own concubine.
I believe that another problem arises from a Romantic preoccupation with an intense, exclusive and (commonly in literary terms) often 'tragic' passion between lovers. This owes a great deal to stories such as those of Aeneas and Dido, and to some of the plays of Euripides (especially those with 'Cretan' connexions). What is forgotten nowadays is that this love was commonly regarded as a 'madness' and as a 'wound' and that it always ended in blood and tears. Perhaps a significant moment in cultural history was when Shalespeare's Romeo and Juliet was transformed into an opera with a happy ending. In earlier societies, to 'be in love' was commonly shameful; even being 'in love' with a spouse. A Greek who was deeply fond of his wife might use the verb philein, which he would also use for his affection for brother or son, rather than eran. Paris flirting with his wife among her maidservants is, as far as Homer is concerned, reprehensible; Hector, who will not even cross the threshold of the room where this is happening (still less sit down beside his sister-in-law and Talk Things Through), is commendable.
The modern concept of the relationship between husband and wife as uniquely, absorbingly, profound, and exclusive of all other deep relationships, is not easily paralleled in earlier societies of which I have any knowledge. The social conditions which have created it have created also and inevitably a matrix in which homosexual partnerships mimic it. That this whole scenario, whether heterosexual or homosexual, has its problems, is suggested by the breakdowns in structured relationships, whether heterosexual or homosexual, formal or informal, which surround us.
It is also worth recalling that the very concepts of 'homosexuality' and 'heterosexuality' are not much more than a century old. The modern assumption of a sexual 'orientation' is anachronistic as far as earlier societies are concerned. In the ancient society to which we have the most extensive literary access, that of ancient Athens, a variety of sexual activities may be described or referred to, but without the modern delimitations. Different actions might be performed by different persons in different contexts and at different stages of their lives, but modern categorisations ('gay', 'straight', 'bi') are unknown, however readily Athenian comic authors might find it dramatically appropriate to mock an individual for a personal predilection.
Such Athenian societies would have regarded as the purest delirium the idea that two men (or two women) should vow and live a 'monogamous' life together. Indeed, I do not find it in the least surprising that more 'advanced' homosexual thinking nowadays also derides this model, argues that homosexuality is inherently promiscuous, and regards the promotion of homosexual patterns of monogamy as being a heterosexual imperialist attack upon - and attempt to control - homosexuals. Given the evidence, and the presuppositions, that view seems to me to have a lot to be said for it.
My argument is that a particular and dominant modern model of 'heterosexual' marriage (or quasi-marriage) is historically atypical, unsustainable in itself, and has done great harm by evoking mirror-image mimicries of itself among people who are deemed to have 'homosexual' 'orientation'. In particular, it has rendered incomprehensible the notion of a deep but asexual relationship.
'Friendship' has become little other than a way of referring to the people one has a drink and a gossip with after work, plays golf with on alternate Saturdays, or has to dinner three or four times a year.