I told her I wanted her to end it with him. She said no.
She said it's not fair of me to ask her to stop, because she has supported all of my flings. Because she gave me plenty of opportunities to put an end to it early on, and I didn't, so now she's too into it. Because she married me in part because of the freedom I offered her... because she would resent me forever if I insisted.
I know I should be kicking her out. I can't bring myself to do so.
She did say some things that calmed me down, though... she said that if she wanted to leave me, she'd be using him to do so - she'd be complaining about me to him, and I know she hasn't done that. She also explained more about her feelings for me, and what being married to me brings for her - things she's valued her entire life that she would lose if we split up.
She also raised the suggestion that I'm only feeling insecure about this because she's so much more successful in her open relationships than I am, and I'm jealous. She might be right about this one.
Then we had some of the best sex ever. I'll have to hold on to how good that made me feel to try to get me through the next few months - while I also seek professional therapy, and possibly anxiety medication.
This will be my last blog post on this forum about this subject. Thanks to everyone for their support.