Open relationships require a number of compromises that don't work for me personally. I had my time screwing anything that walked for decades. To me that was about as open as one could get. I was taught about this in a way I will never forget watching two friends die of complications from HIV. Their lives toward the end was a living hell as one passed first in 1992 and the second one at the hands of incompetent medicine in 1996. Before that time I would have given this board a very different answer than now. I have my moments that I see something that I would like to "sample" like everyone else, but, love and a declared marriage or relationship has to mean something.
When we were first together the rule was that we could do anything we wanted that was not stupid if we were in a gay bar or at some community event that permitted it. What we could not do was to share a bed with another person with our clothing off. If some dude gave me a kiss with some tongue I did not really consider that out and out sex. If that same person started trying to rip of clothing that was different.
Over time the interest in this kind of activity wained and we simply have settled for each other on every level now for more than a decade. It is just a great deal easier.