Feminism applies to both genders, how would switching genders change anything?

You’re really dodging my entire point here. You’re trying to use generic, anecdotal “evidence” to tell individuals that they shouldn’t expect something and should just do it your way.

And I’ve seen plenty of my actual friends go into them being clear about it from the start, communicating fully, and everyone party to it also knowing that a relationship ending naturally is not “falling apart”.

Yes, monogamy is simple and doesn’t require near the same levels of trust and communication(though it fuckin’ should). As a general statement we’re all pretty emotionally stunted and people trying something like that out without the skills to pay the bills are going to have a bad time. On an individual level there are absolutely people who can, and do, handle it really well. All the people I know who participate in open relationships are very emotionally intelligent, honest, and understanding people so it’s no small wonder that they can hack it where others struggle.

No one is asking you to be in an open relationship and it’s totally valid to not want to be in one. You can be all those nice things I mentioned and still prefer monogamy, too.