I really don't think that anyone can rationalise emotions like jealousy- you either feel them or you don't.
I don't really get this "my life revolves around other things.." attitude of SGB- because the two are not mutually exclusive are they? it's a bit of a weak argument to say you are never jealous or possessive becasue well, frankly, I have my mind on other more important/interesting things.
Like what?
It reminds me of the autobiography of Diana Athill- who was highly promiscuous by most people's standards and never married. (She is now 90), though she spent most of her life sleeping with other people's husbands with no qualms. At one point her most permanent partner took a young lover and they all lived togther in one house- very happily.
The criticism levelled against her - by those who read her book- is that she has never really loved. Anyone.
Call me mundane, but even if I stretch my imagination to the limits, I cannot see how anyone who really cares for and loves another person is comfortable with them having sex with someone else.
I suspect that people who say they are very happy to have "opne" relationships simply are not capable of romantic love - or have never experienced it, or build up a barrier so they don't allow themselves to love and possibly be hurt.