I’m pretty sure the blonde is still with the black haired woman and the black haired woman is understanding of the MC.
It wouldn’t make sense for the black haired woman to suddenly get jealous when she literally put her two husbands in the same position.
Poly is about understanding and love and has little room for people being jealous and petty or it won’t work. I think this was dramatic but a fair realism to it. Not all poly are fourways between all, some polys are weirdly intertwined relationships and friendships.
WOW THE LAST PANEL