I think there's a lot more to love and relationships than strict monogamy, and I think the fact that more than half of marriages end in divorce speaks for how effective strict monogamy has been. There are so many other possibilities, so many other approaches to love and relationships that hold the potential to make many people very happy, but society treats them as taboo. They're as natural as our sexualities, and in due course, I expect they will become commonplace. It's about thinking outside the box, outside the bounds of what society considers acceptible and determining whether there's a better solution sitting right under your nose. That is a major theme in Tai's route, from this specific situation, to the lore revealed on Day 3, to the outcomes of other pairings in this route, etc... I simply wish to seed that discussion and hopefully make people think about these sorts of things. I think that kind of out of the box thinking will be crucial in the decades to come.
With that being said, you have your views and I respect that. Therefore, you will also want to avoid Axel and Dom's route as it's a polyamorous route. Lukas' route is strictly monogamous, as is Diego's, assuming of course you avoid the gym.