I have personally always found the thought of exercising the ideal of strict physical monogamy to be exhausting. So much energy required.
I have always been, as have some of the most happily married gay couples I know, monogam-ish.
Strong pair bonding and emotional intimacy matter to me enormously, but setting strict sexual limits on either my partner or myself seems counter productive. Clearly there are perils and pitfalls in a relationship that allows a little sexual freedom and exploration, but there are perils in a physically monogamous marriage too.