Human emotions such as jealousy eat at the fringes of every relationship.
So does the human dislike of feeling limited. There is no kind of
relationship that feels one hundred percent comfortable.
Despite your assertion that something in particular is “required by the
human psyche” — as if there is only one large human psyche out there
controlling all of us — there is no single kind of relationship that
works for everybody.
People therefore create different kinds of relationship, with different
areas of security, different rules and guidelines, and different areas of
Some people create relationships in which loving multiple people
romantically/sexually is allowed — because they strongly want that
freedom; it’s more important to them than avoiding jealousy; and/or they
get more out of it than they put in, in terms of the effort of setting up
a relationship style that’s outside the meanstream.
There are many ways of going about this kind of relationship. Some are
more restrictive and some are less restrictive, depending on the
preferences of the people involved.
Some people don’t want such relationships and prefer monogamy. Or no
romantic relationships at all.
As to the difference between polyamory and open marriage, swinging, and
group marriage: All of these mean very different things to the people who
practice them. But I would say that polyamory encompasses the others to a
degree. Polyamory is simply “openly having multiple sexual and/or romantic
relationships.” That includes open marriages where primary partners have
relationships outside the marriage. It can include swinging, where primary
partners meet others mostly for the purpose of friendly sex. It includes
group marriage, where several people decide to create a life together.
You say those things are “tired relics” and didn’t work. Not so — I know
many people who live all of those lifestyles and are quite happy with them.
I am one of those people. So is my primary partner. Some of us have
maintained long term relationships within those lifestyles.
What *doesn’t* work is when people try to proselytize polyamory, or any of
its subtypes, or any other particular form of relationship, as the One
True Way for people to do relationships. There is no One True Way. That
also means there are fewer Truly Wrong Ways than you might think.