Wow you're up late & pondering deep stuff???? I don't think my brain would be working that late! It usually isn't working this early either!
I don't know if it's the most common way of looking at things but I"ve heard the story quite a few times that someone's s/o is dating a mono person & it turns out that person really just wants the s/o all to themselves! Thinking about it...Breathes' first, second and third s/o's after we got together were like that & didn't like the fact that he wouldn't dump me to be monogamous with them.
Possibly it's different because there is more than two people being hurt by that kind of relationship when one person is poly and has other partners besides the mono one. I'm talking about the closed minded monos, not the ones who are up front about the fact they aren't sure whether they can handle poly or the ones who truly are fine with themselves being mono while their partner is poly. When the poly person comes home from visiting the mono partner there tends to be, at least IME small though it may be, more drama during the reconnection phase. The mono person tends to think more in the me/us two line than in the me, you & you & you line. This then tends to put more drama into the poly relationships because they are trying to deal with concepts so totally opposite to their own way of thinking.
There is nothing wrong with their advocating their needs as long as they clearly understand that just because they are letting their wants & needs be known it doesn't necessarily mean they will get them.
I've heard of poly's going mono and then back again but don't know any personally.
Why am I trying to express myself clearly at 5:15 am???? lol