Thank you so much for your post, MeeraReed. That one helped me even more than the other good ones I've gotten here so far. I do think I've wanted to blame what happened to my ex on the kink in the relationship, but yes, that relationship is also a combination of a manipulative person and an insecure person, and I needed a reminder that such a pairing can be toxic to others in the relationship even without kink.
I also know that I've been inclined to blame my former metamour for what happened, not my ex. I really loved him deeply and it just hurts me less to blame her than him. But you're right. He did treat me like garbage.
I am pretty sure I am not a domme. While I've played at being one a little, I find it much hotter to give up control than to have it in most cases. I'm also not very kinky, I have found very few kink-related things that really excite me. I tend to be attracted to sweet, sensitive men, I don't like cocky men or "bad boys" at all, but my partners haven't all had submissive tendencies. If anything, my husband is sexually dominant, not at all submissive, and I love that about him.
Anyway, I have some happy news. I was talking with a female cyber friend yesterday whom I have known for years, and whose judgement I trust and respect. It turns out that she knows the woman my boyfriend is interested in personally, from back when she lived in the same city and they both participated in the kink community. She told me not to worry about my boyfriend's new friend, that she is a very ethical and responsible woman, and I could be assured that she would neither meddle in my relationship with boyfriend, or hurt him seriously during a play session.
I plan to tell him that I'm Ok hearing about her and their friendship now, although I'd still prefer that he not discuss anything sexual or kink-related he does with her with me, should they get into a physical relationship down the road. Since I know almost nothing about his sex life with his wife (and I've actually been curious about that, but he's volunteered very little about it), this shouldn't be a problem for him.
A big thanks to everyone here for their support and input.