Kinda harsh, but I can see how you would be confused and concerned by my posts, nearly all of which of occurred during intense periods of unhappiness.
My fiance and I dated for several years in high school, broke up and then got back together a number of years later. We've been together for 3 years. We are young, but not that young. We were together a year beofre becoming engaged.
If our relationship had been rock solid with GF, I would likely have stood up to family and taken the consequences. But it wasn't. Far from it. I was looking at trading a huge number of relationships with different people for this one, which barely worked, if you can even call it that. I wanted it to work, I resisted the advice of friends who nay sayed and it just didin't work.
I loved and still love GF. Yet this relationship, especially in retrospect, was bad. I actually made a very valiant effort in the face of much doubt and misery and it was still bad. I could not successfully make her part of my fiance's and I's relationship.
I don't know that I'm poly, I'm okay with my romantic life being slightly blurry around the edges, same for my fiance. I'm bi. But I would never do this like this again.
I was going to avoid talking to him about my feelings, because he is sad, but now I'm think I should anyways.
As for me and my stuff with the wedding. I have a tendency to run away slightly with fantasy. Maybe because I've spent so much time ill and dreaming vividly of nicer things. The stuff with the wedding was exacerbated by the triad, though.
I felt alienated by the relationship and unhappy and would withdraw into the distraction of planning. He would be playng with GF and keeping her happy, without keeping promises to me about getting stuff done. I would get upset at his being a flake. He would withdraw because I was upset that he wasn't helping and that I was in my own head planning and not listening to him enough. With GF, there was something to escape to, things need not have been dealt with with the wedding for him.