... is monogamy natural?
I don't believe that a person should belong to a person.
Even in my most promiscuous times I always made sure my women knew about each other. (That caused a few problems when they became friends)
If you look at the holy books you will see that powerful people didn't restrict themselves to one partner.
Maybe it was all to do with economics and survival. Now it isn't.
Should we be free to have as many friends (with or without benefits) of either sex that we can cope with?