Pitbull
Verboten
Blu, this is rather quite simple. We humans, though fairly stupid for the most part, are rather complex in our make-up. A functional relationship needs to satisfy us on a multitude of fronts - mentally, emotionally, economically, spiritually (for those who think we are spiritual) and yes, physically. It is quite conceivable that two people can satisfy each other in all aspects apart from the physical. If two such people are so inclined, an open relationship could be a workable solution for them.
The bald part is the single reason for steady relationships in todays era.
It's much easier/nicer to have 1 place to stay and 2 incomes. Than 1 place and 1 income.