Some scenarios aren't black and white, especially since relationships are always being renegotiated. I was in a four year monogomous relationship and it was great, but it ended. After that I dated someone for year, who has since left Canada for his studies. We still maintain a relationship via Facebook message and Skype that is more than just friends, but having an online relationship after dating in person is just not the same, so the conditions of the relationship have changed.
I have a good friend who is in a "V" (I think that's what he called it). He's one of two guys dating the same woman. They have their own specific arrangements and he's pretty happy. And this guy went to a catholic high school, is an athlete, and a scholar.
But yeah, I guess this thread is about Ashley Madison, a website I haven't even heard of until now. The internet certainly exposes secrets, not only on an individual level but for social relations in general.