I'm so sorry you are going through that. Its so hard to understand how people can and do have more than one love in their lives. Understanding why someone would suddenly go from mono to poly is kind of like trying to understand why someone would suddenly change their religion I think.
I don't envy your position. I understand what you might be going through and I want to reach out and give you a hug right now. It will be okay. It will always be okay because everything is movement to something better. If you stay grounded in your body, stay fast to your own goals in life, take a deep breath, keep breathing and do your best to empathize as much as you can while using the most reasonable emotional communication you can, you will see through this and come out a better you one day.
Time changes everything. In time you may just see how this will all fit for you in your life and how you will survive and be happy with your relationship life again. There is a lot of work to be done between you and her but most of all the work is in you to do. Finding ways to cope and use what you are going through to benefit you in the future is probably the best you can do right now. Keeping busy on the task of being your own primary is my advice to you. None of us are every alone if we have ourselves. Start thinking of ways you can make this time about you. Find stuff to do that you love to do that you don't get to do when she is around. Make a list of your own goals and start thinking about how to achieve them. Really, she is doing the same in her own way. Be challenged by this new occurrence rather than devastated. Many of us here have been and we are still a live and better for the experience.
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