The complexity of a polyamorous relationship actually makes it more stable if you look at it in terms of the group relationship and not in terms of the individual relations within it. In a triad. a person who is currently dissatisfied with one partner still has a healthy relationship with the other. One has to be dissatisfied with with the relationship as a whole to decide to leave both partners.

I see the somewhat chaotic flux present in the insides of a polyamorous relationship as no different than the trials that monogamous relationships undergo. It is simply the way that it continues to be a relationship beyond encountering those stresses that causes them to stand out.