Slowly, slowly, I've become almost vigilante when it comes to liars and cheats. That's because I've seen it happen with friends and family, as well as experienced the devastating effects of it. I think the lying, betrayal and cheating behind the back of another is a very low act. I don't like the lack of integrity and the dishonesty. It is something I cannot or will not accept in a relationship.
On the other hand, if two people choose to have an 'open' relationship or are into swinging (ie, keys in a bowl...ha ha) then that's their business. It seems to be an accepted lifestyle now but I too think that one person would usually be 'all for it' and the other one 'going along for the ride'. It's not my cup of tea, because I think I'm too conservative for that I'd become the jealous type, but who am I to judge others?