Hey Lexi...Another Great question! And an important one because the interaction between all involved in this lifestyle is more than just the physical sex. Mainly it's the emotional interactions that matter the most, and are harder to describe because each person has a different personality and have different emotional reactions. So I'll try to answer your question as succinctly as I can here in this forum...
Honestly I think age and life experience plays a major role in how all 3 interact with each other. I say that because generally speaking, as we get older we learn what things are not important enough to fight over, and also what things are important enough that compromise is better than fighting.
While all of our personalities are different...(I grew up an only child and didn't have brothers and sisters to fight with, Juli did have brothers and sisters so her personality has been more "vibrant" :-)...still age does mellow us, and we have moved beyond the typical fighting that usually happens in a younger marriage.
So I believe now more than ever that a polyamorous lifestyle is easier for an older throuple. Of course it's not impossible for a younger couple, it's just that emotions typically are more raw and the risk to the marriage can be potentially greater. Not as much for a long term marriage.
It's important for all individuals involved in a poly relationship to understand and accept their roles. To be willing to show a desire for the other's needs and more than our own. The husband and lover especially must put the needs of the wife first. And to accept and stay within certain boundaries so as not to threaten the delicate emotional balance that takes months or years to build.
So to sum up...your question is one that is not often asked but should be. And my answer may not have been articulated well enough to make sense, but I truly believe that because sex between 2, 3 or more people is such an emotionally intense relationship, the effort to be understanding of the needs of the wife, and the needs of the husband and lover as well...becomes imperative. To compromise, submit to our own roles, discard any urges of jealousy...and most of all to love in a way that the men naturally desire the best for the wife. And if the husband and lover both put the wife first...she will naturally fulfill the men's needs...which let's face it, are generally pretty superficial :-)
Mark