Cucking and open relationships just seem like a way of prolonging relationships that should have ended a long time ago. I have my own fucked up fetishes but come on people, don't try to rationalize bullshit.
Open relationships do work. It's a way to prevent people from forcing themselves to stick to one person and one person only. Monogamy isn't actually the norm for humans.
I've never seen one work or heard of one that worked 
There are exceptions, I'm sure. But I wouldn't do it myself.
Like I've said in the past regarding this subject: In the gay world, it's common & you'll find marriages and decades-long relationships that aren't bound by the social trappings of monogamy.
And let's not pull this "a relationship only works if you're only ever committed to one person ever." That definitely explains why divorce is so common.
I'm not making this claim from my own life -- I'm making it from the open relationships I know, from those who are fully open to those who invite a 3rd into the bedroom occasionally -- and on top of that, bonobo monkeys (our closest genetic relative) provide a really solid scientific basis for monogamy not being the de facto experience of human relationships.
What works for you, works for you. Me? I think I'd definitely want something less than monogamous. Life is too short to only be with one person for years and years and years. People wander, men and women alike. If anything, a dedicated open relationship that withstands the test of time is the ultimate test of trust in another person. Beyond monogamy, even.
