Why does their partnership come first? Whats stopping you from finding somebody better to make a priority? Isn’t that the point of being poly is to have the ability to shop around?
It takes work, for both people to compromise, to critically self-evaluate and improve.
When it's easy to just "shop around", you never really have to look hard in the mirror. It's easier to just internally assign blame to the other person: "they're not meeting my needs", and go off seeking someone else who will.
There's value in resilience, in building up your character so that you can endure turmoil.
All relationships have stormy times.
A key facet of emotional maturity is to be able to distinguish climate from weather.