I think it is cheating if it is outside of the agreed-upon boundaries of the relationship. For instance, before my fiance and I had a D/s relationship, he agreed that I could be with other women (with his knowledge), but not other men. So if I'd been with a man, that would have been cheating.

To me, a BDSM relationship between two people, even if it isn't strictly sexual, or even if it's purely online, is a very intimate relationship. I met D online and for the first few months we didn't meet in person, but if one of us had had an SO or spouse during that time, I imagine that they would have been very upset to discover how much time we had spent talking to each other and how close we had become. I'm very happy that we were single when we found each other.

Personally, I go by the "golden rule." I have male friends online and in person, and when I am with them I try to not do or say (or let them do or say) anything that would upset me if D did that with a female friend -- so a hug is ok, but a kiss definitely is not. For me, a BDSM relationship falls into the category of something that would upset me if I was the spouse. I would be badly hurt if I found out that the person I loved had gone behind my back to find a relationship with such a deep level of trust and intimacy -- even if there was no sex involved, I think it would be worse for me than if he was just sleeping with someone.

Of course, there are people who have multiple relationships where everybody involved knows, and they all seem happy. I really admire those people (I'm looking at you, Wolven Vixen) for their generosity in "sharing" someone important to them -- I don't think I could ever do that.

Also, I think part of the reason that there is such a stigma attached to homosexuality, bisexuality, and sexual fetish lifestyles is the stereotype that people get married as a "cover" and then cheat in order to satisfy their "cravings." So even though a relationship between two consenting adults doesn't hurt anyone in and of itself, a lot of the time there is someone on the "outside" who is hurt -- and moreso if kids are involved.

I don't want to judge other people, because I'm so lucky myself -- I love someone, he loves me, he seems happy to dominate me (after some initial stumbles), and neither of us are entangled with other people. I can see how the choices get really complicated for people in different situations.