|Ok. So, first things first, it was long. Which isn't a bad thing at all, as it was an enjoyable read.
Second the beginning was a bit confusing to me. It seemed a lot was happening, and some of that information is never used again.
Also you use the terms "polyamorous" and "Monogamist"
But you don't explain what either are. You give examples after the word is used so the meaning can be inferred. However I feel like if you could work some sort of explanation. Perhaps in the "blurb section" of their meanings it would be very helpful.
Moving on. I do like Seto's portrayal. It feels very researched and polished as well. It's clear you did your homework, and care deeply about it.
I genuinely laughed at the Kuriboh plushie punishment. That was a very nice touch.
Finally the whole scene in the dress shop. When the employee tells Marc he has to leave. It was very abrupt, with no real context. At least not until after the incident. Where he mentions it was racial. Perhaps include that in the the initial encounter.
So all in all. It was an enjoyable story, with a good storyline, but you should just clear up a few things. To make it an easier read for less Adept readers.