I'm a sub, but I'll throw my 2 cents in. My Master and I are monogamous. He has said he has no interest in being with anyone else. Same with me. I'm extremely territorial and jealous, there is no way in hell I'd share myself or him.

The poly/multiple thing does happen a lot in the D/s world. However, I know I was surprised by how few people actually practice this. I'm sure you will be on the same boat I was. A big turn off of the lifestyle for me, for a long time, was the idea that I would have to share my Master when I had one. After I got to know some people in the lifestyle and learned more about it, I realized my previous perceptions were incorrect. I hope that the wonderful people here chime in with their thoughts.

Yes there are people who have multiple subs and while it's common enough, it's not always true of all Doms.