For me it is very simple, Trsut needs no system. I am not a platonic thinker but it is very much practi. Secondly Marriage System is very much gender discriminatory where women has been given not only lower position but also treated as an instrument for pleasure than human being...
Someday there is need to do research as who goes for multiple partners... is it married one or Live-in one. But in today's society married ppl 'go out'....