I liked some posts accidentally on here, but my like on yours was intentional... I understand where you're coming from. Personally I've dealt with feelings of possessiveness stemming from jealousy, but I never externalised that. In my case, monogamy is the best option for me because it's how I work, I want to be with only one person and hopefully that person will like me back and enjoy my company as well. I don't feel a need to bring more than one person to the relationship because again, it's not my thing and navigating a relationship with a single partner is complicated enough. I would probably have a meltdown dealing with a different arrangement.
Another thing is that to me, sex is not a purely physical act, but an emotional and metaphysical one. I've had casual experiences and absolutely hated them, felt empty afterwards.
I don't believe that I own the person I love romantically. Nobody owns anyone and free will exists.
I'm not going to delve into other forms of love aside from romantic, but I think there are different kinds.
I guess everyone has their own way of living, again, we should just accept that even if it's hard to wrap our minds around it.