Responses
It's an interesting relationship. I think Yuu would actually prefer for Kou and Ginga to have feelings for each other too which (SPOILER ALERT) it shows they do in the sequel. It truly is a poly relationship but with certain preferences. Mainly the two alphas putting Yuu first before each other and it works well for the three.
Question is...was there ever a time Kou ever bottomed? Don't recall if they hinted that too.
I’m glad Yuu chose Ginga and Kou and could bond with them, too. If he had chosen only Kou, Ginga would’ve been damaged beyond repair. Completely broken. So I am very glad that it turned into a poly love. Also, it is obvious that Yuu comes first for both Kou and Ginga in everything.
To clarify, they did not cheat on Yuu. They slept together to ease the heartbreak of Yuu constantly choosing anyone but them. They understood each other’s pain and heartbreak and sought solace from each other. Also, Yuu did find out about it at the doctor’s office and didn’t care. I think he was more fascinated by it. (⌒▽⌒)