Hi there, I'm sorry you are struggling. At least you are in good company. Many people come here with the same concerns in the same situation.
I suggest that you make sure she knows that you need TONS of support to get through this and that it is of the utmost importance that she do her best to stick to her agreements and attend herself to as many of your boundaries as she can. If there are any that are a real concern for her than do your best to adjust to that and find a compromise until such time as it doesn't matter any more or it needs to change again.
The best thing I can think of is to be as honest and forthright with your communication as you possibly can. Ask for their patience, love, support, listening ear and consideration at ever turn. It is okay that you struggle and the more that they attend to your need for reassurance the quicker you will be able to trust and get through these feelings.
You won't be able to, I don't think, unless you are communicating and continuing to ask for your needs to be met. They should be doing the same thing in order for this to work. I know that is hard, but completely necessary. You aren't being selfish by doing this, you are giving them the gift of being able to understand and support you. I'm sure you would do the same no?
I also suggest going about doing what YOU want to do in life. Get going on a project that you love that is for you, find some new friends, go out to poly community events in your area and continue to work on your own stuff. There is nothing like feeling good about your self to get through the kind of feelings you describe in my experience.
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