Responses
The reason people are pissed ain't because it's polyamory. It's more because of the fact that Nao actually didn't have any romantic or sexual attraction to Subaru, at all. But he was indeed in love with Azusa and Subaru just forced his way in in their relationship.
Some comments angry at the relationship, polyamory is real get over it (●'◡'●)ﾉ