Interesting question. I guess it depends on the level of the relationship. For instance. Tojo, you indicate this submissive that you own, you are not in any kind on sexual relationship with her. This would be partly due to you being married to your wife I assume, and your devotion to your wife keeps you from making the relationship with the submissive sexual (just an assumption).

I have played with many submissives, and each time I play with one that is not my wife/slave, the play, although sexual in nature, does not involve sex. However, your talking about a D/s relationship vs a M/s relationship. The dynamics of each are quite different. In a D/s relationship it submissive is there for the servitude and submission, and some D/s relationships do not include any physical punishment, only mental, or chores.

So can a D/s relationship exist without sex? Yes, but as the level of the relationship increases, I would guess the people involved would desire to include areas of intimacy that one would normally expect when in a long term relationship.