Not all people who are in a relationship love each other
Then I don't really see the point in being in a relationship.
Do you mean you are not allowed to be sad if your FWB arrangement ends?
You can feel however the fuck you like but if your husband called you one day and said "Really sorry but this isn't working for me, I want to stop seeing you" you'd feel a lot more hurt than if your FwB did the same. Of course you might feel a bit deflated but, ultimately, neither of you had made a commitment, hadn't become emotionally involved so why would you feel sad?
Not all relationships are exclusive
Well, I think that's a wider debate to be had. But, either way, if you're in a relationship but still fuck other people your relationship is still your "central" relationship IYSWIM. The other men are just flings/bit on the side. FwB isn't like that as there is no "central" relationship.
No obligations just seems another way of saying you do not have to have any regard for their feelings
Kind of, yes. In my early 20s I didn't have the time, inclination or head space to care about anyone else's lives/feelings/problems. What I meant more than obligations about feelings was obligations like meeting family, going to family weddings, spending every weekend together. Relationships are about give-and-take, when I had FwB, I had absolutely no desire to "give" my time/space/life/emotions.
We are not going to have sex again - don't be sad, you knew what you were getting in to. I am making out with your friend in front of you - don't complain, we are only FWBs
Yeah, that's basically it.
Lots of relationships do not envisage a long term future together
But with an FwB you don't necessarily even envisage a short-term together. It's fun for now but in 2, 3, 5 years who knows!