I am finding this very interesting, this conversation.
Having attempted a veto before in my relationship and it ending up being a decision that PN made himself I think I know a bit about it. I have come to realize that I can't see how veto power would sustain a relationship. I used to think that but then I'm a bit of a dominant and in D/s this could he sustainable I think. Only because all parties agree though.
Now I think that I would put my partner ahead of myself in the form of a compromise for a short period of time. Then negotiations would have to begin again as compromise doesn't last either and should not be a goal I think. Veto is essentially a compromise perhaps? If a partner asks us to end it with someone then we would consider compromising our feelings in order to do so. If we asked them we would be requesting a compromise from them so that we can feel sane again. I can't see how this would be sustained for long. There is just too much at stake in asking for a long term compromise from anyone. Eventually I would think it would rot the foundation of a once well built relationship... hopefully some kind of restoration could occur before that happens. Of course that would mean patience and perseverance. Something that I don't think comes with being firmly of mind that relationships are only workable if they are a certain way... the interest for me is in the wonder of what will happen next and the excitement of the challenge of making a relationship (along with my partners excitement too and their desire to make something of "us") the best it can be...
On another note, I get the whole prescriptive/descriptive thing now btw... I'm pretty sure this thread is filled with me figuring it out. Ya, got it now
On another note, I have two primaries and it is totally possible. I don't think it could be, for me, unless a triad type of connection happens though. Although my two men are not sexual, their connection is what makes it possible for me to have two primaries. They slowly have merged their lives and what I had with PN is no longer, what I had with Mono is no longer, what we all have together is new and a result of what was. My one primary relationship is made up of two men.