omg finally someone i can share this brief list with. I feel like its taboo in a lot of places and not just in Asia, making it hard to find stories like this in general. I'll add The Naked Kitchen to my list, thanks!
A Bizarre Love Triangle has a complicated story that includes SPOILERS cheating and rape, but eventually has a polyamorous story
Between Complete and Incomplete is a canon polyamorous relationship. They use the word "polyamorous" to describe the relationship.
Hello My Love has an open ending where it's not clear if they end up polyamorous, but it could be interpreted that way.
Jealousy Incarnate has a few episodes where they are in a polyamorous relationship, but it isn't necessarily done in the best way and is short lived.
5 Sense Eros this doesn't have polyamory, but it does have swinging.
Stuff I haven't watched but might be polyamorous:
A Crowd of Three
Best Wedding
Love Shuffle I would guess this is more of a swinging thing than polyamory