I really don't think such labels and designations as primary, secondary, or co-primary are all that important in this situation. There is equal and there is fair and there is equanimity - they aren't all the same thing. If I were you, I would back off a bit on reiterating your desire to have everything be "equal." Kathy has invested a lot into her relationship with you - it could seem an insult for you to keep asserting that Rita have the same place in your life that she does. I also think that you can afford to let go of the fantasy that you all live together for now. Being equal, living together, developing friendships, regaining trust -- these are all things that can only happen over time, and with a lot of hard work, soul-searching, commitment, and honest communication.
Worrying about the structure is a bass-ackwards way to approach it. People are people and structures arise out of what people want and how they feel best interacting. It is usually a futile attempt to try and set up a structure first and expect people to fit into it. You need to worry about the relationships first.
Who knows - you, Kathy, and Rita could arrive at an arrangement that you would never have imagined, so stop thinking in terms of where and how they will fit into your pictures of what you think would be a great situation, and let the relationships evolve and morph into something that is right for all involved. Because you really can't control these things, and it always seems to backfire for those people who say things like, "I want a triad, so I'm going to find people (or ask people already in my life) to insert into this dream triad of mine, and they have to make it work." Kablooey!
The first things you need to do is work on regaining Kathy's trust and letting them build their friendship as they see fit.
Last edited by nycindie; 05-21-2012 at 11:51 PM.