I think you need to construct what you want to say a little better, especially with the paragraphs being too long and convoluted. It's like a stream of thoughts.
But the gist of it seems to be there are lots of arguments and people not knowing what they really want. If there are a lot of arguments it means people are bad communicators or with people that have different values than them.
People can change their values, it happens all the time. You just need the right education vehicle to do it. However people that have reacted irrationally over a long period of time have pretty much shown their cards already, that's pretty much what you can look forward to. Sounds like someone in this triad needs to put their foot down and no one is willing to do it.
I would simply say to her, you aren't going to see "US" again unless you get with the program. And the "US" needs to be united on it, not this going behind the back crap and having secret sessions. If you can't find an "US" with your guy, get rid of him and start fresh.