You HAVE to merge...
Of course all relationships, especially those that come about in later years have to find a way to merge out of old thinking into new. I don't think I can understand how people in poly relationships can establish and maintain a healthy, respectful union if they are finding partners that are not likewise already "merged" together?
For example: If I meet a man who I am interested in, that accepts the idea that my husband is my "primary"- how can expect him to merge into a relationship with us and possibly someone my husband has met with the same respect I have for my husband? Obviously the first attraction was me, so, wouldn't that be his agenda? For me, the only way a poly life can work is for two already established (or six) couples to mesh- being already merged in some sense... does that seem to hold true for most people?