Flowerchild-in our dynamic, who gets seniority is the household (there were four of us adults, now there are three).
No reason except-we live here. Doesn't matter who is or isn't romantically involved with who (not all have been romantically involved).
If someone in the household is being a pita, family meeting time. Period.
But there is no "kicking someone out of hte family". It's a matter of whose IN THE HOME. Because our home is our sanctuary and it needs to remain a sanctuary for all.
There was a year I did not live in it (as the wife) and there was a time Dh didn't live in it. If one can't manage to function to the best interests of the children and other adults in the home-they need to leave until such time as they can.
It doesn't matter who screwed who for how long.
The "seniority" within the household is the kids. Not any one configuration of adults.
"Love As Thou Wilt"