Well... as one who does and encourages mine to both play and satisfy herself, with only a few prohibitions, one which I also practice... (actually two ) I can speak from the other perspective VaAugusta.

But I see your point, most dominants tend to not share. I wouldn't share my car... but then it doesn't have a brain and can't take care of itself when being misused...

The right answer, imo, for spicennice, is to point out that D/s and poly (multiple partner) are two separate topics and two separate points of conversation.

My vanilla wife and I are poly (to an extent) but she has zero interest in D/s or any type of bdsm. And many many bdsm lifestylers are 100% monogamous, male and female included, dominant and submissive included.

As they are two separate topics, you should have the two conversations... and quite frankly, you discuss poly first. If that has already happened and the dom is insistent, you may well be with the wrong person.