Ugh Saku is actively trying to get himself NTRed, man he could have it all, and yet he has the worst fetish.
But in a way, by having the worst fetish there's no way for him to lose in any relationship, whatever the outcome he wins.
Edit:
@MrMcNasty The only one that would suffer from a break out would be Amane, they don't actually love each other, they were pity fucking each other, but if they could they would date someone else, If Amane catches them, so what? will she walk away and miss out on the only chance she has to have sex with the man she is actually interested in? of course not, Susa is not her boyfriend he is just a ticked that allows her to have sex with her crush.
And for Susa, it is true his only value is that he has a big dick, and now that big dick is getting him laid, and closer to the women he is interested in, as a human dildo but that's enough for him, he knows he is just a sex toy with legs, for him and his goals Amane no longer plays much of a roll, specially because Saku already plans on having Susa NTRing him, and Iruka also wants him fucking Miko, Susa has successfully entered Susa's and Miko's swinger circle, and can stay there regardless of Amano's approval.