I just have to say, my heart goes out to you. Not many people would be as kind as you are being in this situation. K is a lot of words I can't say on here, but most of all she is the one manipulating you. On your first post, I believed she wanted some sort of sister wife situation, including you on this relationship. I now see she wants to have your blessings for her to cheat on you. Her actions are completely unacceptable and you should not put up with it for another second. You need to listen to your emotions and heed their warning that this is not ok in any way, shape, or form. She is playing a game with your heart and that is totally wrong.

I know it is easy for someone to say leave her, but is that a possibility? Can you reach out to a friend? It cant hurt to try. Also, if you need support, maybe there are free support groups for something like this. Check out meetup. A divorce and separation group or a cheaters group might be helpful to you.

You are right, your relationship with her will never be the same. So whatever you decide to do just know that you deserve better than this!!!