Opalescent, I prefer not to have a relationship with the potential metamour because I have trust issues in situations where the metamour is a dominant. I don't like the power they can wield, and I have been in a situation where my partner gave a dominant metamour too much power and she chose to use it against me with disastrous results. A similar thing also happened recently to my best buddy, his girlfriend acquired a dom, the dom said "Get rid of your other partners," and she rushed to do his bidding. My friend, who had been devoted to her for two years, got tossed aside like yesterday's garbage.
So now, I choose not to date submissives. My OSO is not one (I think). He's just met a woman he thinks is cool who happens to be a domme. I communicated my misgivings to him, and he is going ahead anyway, which is his prerogative, he's an adult.
Anneintherain and MonoVCPHG, thanks for your words of support. I feel much better about my decision now.