I perfectly understand some people being surprised about Yoshihara, the writer of Ai no kusabi, being a housewife. But I find that when you look at some things in the novel with that in mind, some aspects of the work make a lot more sense. Of course I don't know Yoshihara personally, and my observations may be completely incorrect, but I find that Riki’s dilemma of "being caught between two feelings of different nature" (as Yoshihara puts it in an interview) makes a lot of sense when you have in mind the repression a housewife of her time had.
These feelings that Yoshihara talks about are his feelings towards Guy and Iason, respectively. These feelings represent in the story two different things for Riki: Guy represents Riki’s "social duty and the duty towards the family." The relationship Riki has with Guy is what is socially seen as aceptable, is what Riki ideally should want. At the same time, Guy also represents the family. He has known Riki since they were kids, and Riki owes him a lot from what all he has done for him. Iason, on the other hand, represents Riki’s true nature: his sexual awakening and sexuality.
Ai no kusabi main conflict is about "duty vs desire" and the conflict between two important parts of Riki as a person that Riki refuses to leave behind. In the end, Riki chooses to stay true to himself by both fulfilling his duty towards his family (saving Guy) and not leaving Iason to die alone and dying by his side, completely embracing his true self.
I think if we closely observe how these themes are portrayed, it makes sense why Yoshihara would write them like this. A housewife sacrifices a lot for her family: sacrificing her own desires and her own individual identity. But while it's easy to say to simply abandon your family to live your truth, you can not simply discard your family: they are your duty, and they depend on you. You feel like you have to stay by their side, even if that means losing a part of yourself. The ending in Ai no kusabi is an idealized resolution to the conflict: Riki fulfills his duty to Guy, while also being ultimately loyal to himself, and choosing death with Iason, that symbolizes he commitment to his found identity.