I appreciate all the thoughtful responses.
A few other major red flags cropped up as well, so after two years, I have put my heart into protective mode and stepped back.
So far back, I question if I will ever live a poly life again actually, though I know the concerns that have me broken hearted are related more to character than to poly...
Sunshine and I do have a counselor session lined up to discuss how our relationship came to this, and to explore how to transition to platonic loving friends.
Me - self defined as monogamish: currently physically monoganous, emotionally poly
Sunshine - my committed partner, poly, married to S
S - my metamour, poly, married to Sunshine, multiple partners