her "lover" is a "master" she met online. I hate D/S stuff. Can't do it, don't like it. So I've been great that that need is met for her. They've had sex a few times. But he has no feelings for her. HE is not even attracted to her per se. He simply gets off on having lots of women he plays with (almost all entirely online except my wife). She is one (of many) toy(s) for him. He is also rather poorly off in real life. I think she may feel a kind of Florence Nightingale effect for him.
Egad, what is she thinking! It sounds like she is caught up in the excitement of the D/s too much to see who she is really dealing with. Love? Oy veh.
While I could never relate to the original agreement you had, as my mindset is very far from that of a swinger's, and I do always think there should be room for the possibility of love to blossom when people get involved with numerous partners, I think AT is right when he said she shouldn't have foisted poly on you. It was rather mean and inconsiderate of her to just flat out say, "The rules suck because I don't want to play by them anymore, and I won't." There should have been a talk, "Hey, this isn't working for me anymore, I want us to reconsider our boundaries, allow for some feelings, can we take a step in that direction," etc., and go slowly, with consideration,
if you consented.
the fact that it hurts me, she says, would make her feel guilty. To stay with me, I have to NOT BE HURT by what she's doing.
She has convoluted some important basics. Yes, we are all responsible for our own feelings. It is true that your feeling hurt is, to a degree, a choice. By that I mean, people don't
make us feel anything. We have thoughts and belief systems that influence our reactions to events and prompt feelings to arise in us. One person can say or do the same thing with ten different people and those people will each have their own unique responses and emotions regarding it. So, no, you don't
have to feel hurt by her loving someone else (if this is love), and she did not hurt you. She admitted to having feelings that you and she agreed neither of you would entertain, and you feel hurt because of thoughts you have surrounding her actions, which is different from saying she hurt you. But now that hurt is very real, so you have to deal with it. However, she can't then realistically expect to turn around and say your feelings will make her feel guilty. Feeling guilty is her choice! She wants you to take responsibility for your feelings but she won't take responsibility for hers. That is just a manipulation.
Have you ever had any interactions or conversations with that Dom? Does he know you? Just wondering. She didn't move out, did she? Is she talking to you? I think therapy may be a good step for both of you to do together.