How to set up polygamous BF/GF relationships (as opposed to casual sex or FWBs)?

[The Byronic Man]

I'm a bit confused here.

I know that casual sex can be maintained by not seeing her more than once a week. But what about actual BF/GF relationships where you can see other women? That sounds like the type of relationships what Chase espouses.

1. How exactly do you set up these BF/GF polygamous relationships?
2. How are they different from FWBs?
3. If you have a partner for casual sex/as a FWB, how do you convert that to a polygamous BF/GF relationship?