I think the problem is--feelings may be genuine and deep. But as you say, time is finite. Resources are finite. You can give the home, the shared life, the shared bank account, the life insurance, the promise to retire together, the health insurance, the legal acknowledgement to one person or another.
Yep. This is it, precisely. Our entire society, including many of its rights and entitlements and privileges, is built around monogamous couples bound in the institution of marriage.
That has its advantages as well as its disadvantages but, in any case, it's a powerful institution that tends to perpetuate itself and quash dissent.
I consider myself well and truly quashed.
To borrow a metaphor sometimes applied to other kinds of systems, the institution of monogamy has a strong electromagnetic field around it that tends to pull things back into alignment if they drift askew.
These days, I tend to focus on the advantages of the institution, as it can foster "care-taking, faith-keeping, kindness, neighborliness, and peace" (as
Wendell Berry puts it) against the ravages of selfishness and raw libido.
As individuals acting entirely on our own
feelings and
needs and
desires, it's difficult to maintain the kind of steadfastness that social cohesion and basic human decency requires. Institutions, at their best, serve to keep us on track, to steady us from outside.
Not perfectly, of course; never perfectly.
But until and unless the institution of marriage itself changes - through the emergence of a new society-wide consensus and the crafting of new laws and norms of conduct - any attempt
by people already married to practice polyamory while remaining decent human beings to all involved will be an exercise in futility.
As for the advantages of monogamy, well, like the song says, you don't know what you've got 'til it's gone.