Most so-called open relationships aren't remotely what I think that is supposed to mean. In most cases, they are some variation of something warped, like him whoring his wife out for warped sexual thrills or running around on her and having more polite language for it.
The problem with trying to have an open relationship is that it's not socially acceptable, so it usually isn't advertised which means if they are married, it's typically a secret agreement between two people with legal protections that allow them to refuse to testify against each other and this often means they are playing sick games that involve jerking around outsiders who aren't being given sufficient information for it to qualify as informed consent.
In other words, they are often deceiving other people in some way and what the other parties THINK they are agreeing to is not what they are really agreeing to.
I've thought a lot about such things but for now that's the only point I wish to make. That doesn't mean my views are entirely negative.
It just means that I think that "90 percent of everything is CRAP," including 90 percent of so-called open relationships.