it does work for some people, firstly because all of this in love stuff...well i have to ask, what is it really? most people will say they have been ''in love'' and ''have loved'' more than once and with each new partner will say they have never before loved anyone like they love them etc etc , that to me is because everyone cares about and likes admires etc each individual they become close to in totally different ways ..so why cant you love more than one person at a time?
what causes the problems with poly r/ships is nothing to do with love or lack of it but just plain jealousy imo
at a fetish fair we went to last year we met a family.
in all there were 7 members each with their own place in the household and they'd had been together for some 20+yrs they were all extremely happy and each were equally of value, however i think thats fairly unique.

i said 7 members but you might want to (yet strangely they didnt) include the married ''cat'' who came to visit once every week or so for a little 10 minute petting on someones lap lol