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.
I guess I wasn't clear. In my polyamorous relationship (which is not an open poly, but more of a polyfidelity), I've found that having relationships with the same people that someone you are fighting with has relationships with keeps the fight from getting to the point of separation. A fight that may cause someone to leave your life instead causes them to keep their distance for some time.
I think of it as the other relationships you share attenuating the relationship stresses such that you are not torn apart from each other. Afterwards, they hold you in proximity like stitches on a wound, to allow you to heal.