One of my good friends described a certain amount of equality this way: If the established partner said, "I'm feeling a bit insecure at the moment, could you spend less time with our new partner so we can work on it?", could that situation be reversed where the new partner said, "I'm feeling insecure at the moment. Could you spend less time with your established partner so we can work on it?"
I don't want to sound bitter... but Amen to that. I absolutely respect the relationship between my partners, and I believe in them maintaining that relationship, but not at a cost to my own emotional well-being.
I used to think it was because I wanted to be put first. Not always, but occasionally. Then I would feel guilty about wanting to be put first. I knew what I was walking into when I entered this relationship. My partners were definitely an established couple, and I was the one who joined them.
I have come to realize it wasn't about me being first, it was about being a part of the relationship. That what I have to say has value and meaning. That my feelings are no less valid then anyone else in our relationship. For a very long time, I didn't think I had a voice, and sometimes still feel like I don't. It really sucks to be left guessing as to what the other is thinking. Everyone is entitled to their own thoughts and feelings. But if those thoughts and feelings aren't expressed, then you are left to fill in the blanks.
I really feel your pain Coeli. I know that at anytime I could be facing the same situation as you.