As another poly person, I agree with your intellectual points. Also, your understanding of the reality of the lie that is, the expectation that a monogamous relationship (or any relationship) will bring stability on its own, is a valid emotional reason for you to be polyamorous.

However, I don't think it's fair to assign all this pain to just the shitty normative expectations that you're talking about.

All breakups hurt. They just hurt.

When people are hurt, they're messy, and they're trying their best to make sense of their situation.

Yeah, their tools for understanding the situation after the fact, may be bad, and not help them heal as well over time, but a lot of this hurt is normal and healthy to feel. It's normal for shitty things like a breakup to be shitty.

Good knowledge of self, understanding of emotions, and the self work that is required for non-standard relationship structures, is a godsend for the period after, for slow thought, coming to terms with a change, all those things.

But the pain of loss is its own thing. Nothing we, nor any societal structures can do about that.