The nasty truth is that historically novels that deal with such themes belong to the genre of pederastic fiction, which because of how same-sex attraction (notion I don't say "homosexuality") has worked until we went and made an identity of it due to it being pathologized by psychiatry at the end of the 19th century, includes a lot of early queer literature like Doria Grey etc. Examples here include Tony Duvert as do highly influential gay schoolboy novel Les amitiés particulières by Roger Peyrefitte (don't look up his private life good god) which, through its movie adaptation, has influenced a lot of how homoaffective and homoerotic relationships are portrayed in shoujo manga. Point is, most books that depict such things, and there are quite a few, tend to focus entirely on the pederast of which they usually tend to view with good eyes, because they were usually written by one, as was common because while a dirty secret, the notion of the "initiatory same-sex relationship" continued well past the Christianization of Europe and was extremely common in the medieval period and down to around, more or less, the early 20th century, when these things were increasingly pathologized. You may understand it as a deep-seated remain of very ancient Indo-European practices in our culture.

I don't think such novels, then, can be really compared with Kaze to Ki no Uta and specially not Loveless, with the former you still have an aesthetic argument: the matter of fact is, these novels from the early down to the mid 20th century were extremely influential in shaping it, but rather than portraying a positive pederastic relationship, it is the chaster relationship between boys which is seen as good, and that of Auguste and Gilbert is not even pederastic but pedophilic, incestuous and extremely destructive to Gilbert. Although it is certainly eroticized, this is not anything any such novels portrayed.

The successors of Kaze to Ki no Uta, in the magazine JUNE (I translated a story from it! check my pinned!), featured almost exclusively older dandies with beautiful boy, bishounen, and while erotic, it is also fundamentally a deviants' magazine: stories frequently have sadism, murder, even necrophilia is oddly recurring. It is a magazine of aestheticist decadence that takes after the late 19th century decadentist literature, not something interested in dynamics necessarily.

As for Loveless, this has to be understood: it is fundamentally a story from the POV of a child who has already been groomed by his brother and is now having that continue by an adult who does not even know he is doing it because he's that fucked in the head. It is not a manga not really about relationships between older men and younger boys as much as it is about CSA, loss of innocence, trauma, broken homes, parentification, perceptions of sexual experience and its correlation with maturity (hence the famous kitty ears), etc. Part of the point is that although Ritsuka is never raped, unlike Gilbert, the things Seimei does very much count as molestation and this is felt in his psyche. It is all experienced from Ritsuka's pov, who nonetheless despite his gloomy 2000s emo looks, continues on trying to do his best and getting friends his own age, which contrast with his dysfunctional relationships with adults and his brother. In short, a novel that handles themes of CSA as extensively and sensitively as Loveless while also not being solely about it, I am not aware.

As for fiction which portrays such relationships in its appropriate historical context, see Mary Renault's The Persian Boy (and many others of hers), Eromenos - A Novel of Antinous and Hadrian by Melanie McDonald, the self-published Another Way of Being by Sion Liscannor, and for a specially critical, non-romanticized one see the very recent Sporus duology by S.P. Somtow, about the infamous case of Sporus', emperor Neros' castrated and horrifically force-feminized literal boywife who was turned into his emperatrix because he happened to look like Neros' wife.

A little aside, while Sporus is indeed the most infamous case of an emperor's eromenos, it was disruptive for other reasons: making his eromenos imperatrix made it that he had immense power, and thus immense power over many "real men" which did not take kindly being subjected to the power of a pretty boy turned empress. Two other disruptive eromenos relationships were that of Antinous with Hadrian, this one due to the latter's excessive grief at the early death of the former, and the very obscure Earinus, Domitian's beloved boy, where the issue was that Domitian quite simply respected him too much lol: he valued his counsel, which now meant that an eunuch was above both general, politician and poet, all the manly occupations of Rome; Poets had to write praise poetry on Earinus' commission, who wanted to commemorate his relationship with the emperor, which could've only felt like an emasculation to men like Martial and Statius, who wrote those poems from which we know of Earinus. Domitian listened to his counsel, treated him as an equal and reportedly even Domitian's wife liked the boy. Eventually Domitian gave him the status of a freedman, and he may have a formed his own family due to this close romantic friendship with Domitian. Hilariously, Domitian, who famously tried to create a cult of personality around himself as a ruthlessly moralistic censor, had banned all castration of slaves and all child prοstιtμtiοn. One of the verses in a poem of Statius amounts to "you were just the slightest bit too late, Apollo willed it that you would be beautiful". This is actually the most disruptive one of them all, rivaling Sporus, because the extreme respect shown to his eunuch boy by Domitian had the side-effect of, well, making an eunuch de facto more elevated than all the manly men in the land. About Earinus there is no fiction at all, though if you ask me this is a shame, he is an exceedingly interesting character.