Ah! ~rubs hands together~
Let's delve into this... you make some interesting points...
This is going to be long - I apologise.
Poly isn't just about jealousy
You are right - two of the main components in poly or any kind of relationship are honesty and communication. But I do believe there are another two elements.
When I (personally) consider whether I contain the muster that is required for the enlightening life o'poly, I keep those four points in mind:
honesty, communication, compassion and saturation.
By saturation, I literally mean "How much can I take? How many issues? How many people?"
You know your saturation point. But is your saturation point
effective for you? Is it causing problems in your relationships? Could your relationships be better if you were able to loosen your saturation point?
I absolutely understand that your perspective comes from that of the third party in many relationships and that you had that horrid issue with your husband. I do of course, absolutely understand your perspective and I am truly sorry that you had to go through that situation with your daughter.
Travelling as a group
You feel that because you have a finely tuned communication and jealousy engine (and honestly, that is great), you're ready to hop in the Poly Wagon. But, let's say your empathy tank is running on empty, because you've thought about others your whole life and god damn it, it's your turn to be thought about. Should you fill that up before you get on the road? Can you start driving and let others help you fill it up as you go?
It's good that you know what you expect. I like strong women. Strong women make the world go round. But sometimes, we fail to feel the world quivering as we take it by the balls.
Ask yourself a new question, taking the example of "crazy angry wife" from last night:
"Did I effectively check their motor before I got in the back seat?"
How long have they been poly/open/whatever they are? Do they have guidelines? Did naughty husband break any of these guidelines? Have you met both of them? Is most of your interaction with the husband?
Maybe you asked all of these things and they seemed good on paper. You can't foresee problems sometimes. Occasionally, people are just crazies and they hide it well
But if this is a pattern for you, that other people always seem to have more issues than you do, you could examine that more closely.
If you hop in the car and say "let's drive - but I won't tolerate any discomfort"... what happens if someone wants the window down? Are they likely to raise the issue? Or are they likely to make death eyes at you because they are too hot? Most likely, they'll hit you on the back of the head whilst condemning themselves for being too hot... everyone else is comfortable, why aren't I? If you get in the car and say "sweethearts, we've never taken a road trip together, let me know if you need the window down" you might have a merrier trip.
That being said. If one awkward passenger wants the music up, the window down, to drop fast food all over the seat, to kick the back of your chair... then yes, of course it's ok to jump out of the car.
What you can do is be really clear, yet compassionate, about the state of your motor before you all take a trip. "You should know, I struggle to have patience with jealousy
because..." "I like you, but I am nervous to enter a relationship with you if you are new to poly,
because..." etc. If you want to date couples, your end of the bargain is to be considerate whilst they make room on the water bed for you.
Then look at their engine from the outside of the car. Even if they say it's fine. Look beyond what they tell you.
Changing patterns
It's interesting that you say that the third in a triad is often the first out. Also, that the third catches the brunt of the BS. Has this happened to you many times? Could there be any repetition of behaviour from yourself there that led to this? In my experience, there's always something we could have done differently ourselves.
To me, dating is like house hunting. You might want a penthouse, but you can't afford it. Maybe you can afford it, but you can't find exactly what you want pre-made. So you live on a construction-site for a while whilst you make home improvements. In short - if you haven't found what you're looking for, maybe you can stick around to create what you're looking for.... or shift your expectations. Or, wait a long time for the perfect one to come up.
I would definitely suggest, if you want my advice (you may just be looking to date me ~wiggles eyebrows~) that nobody likes too much drama. It's a headache. You don't have to put up with mountains of stress. But just ask yourself - can you compromise and if so, could you be happier for it? Or are you really always getting involved with heavily-issue-riddled people? If so, why? What can you do to change that pattern? Are you actually in a better position than most, because you have the experience to lend to other people, rather than the blind leading the blind? Or will you only settle for someone exactly the same as you, however long it takes? There's no right or wrong.