Responses

Yes it's possible. It's called a polyamorous relationship. The difference between a poly relationship and cheating is that partners involved in a poly relationship are aware, informed, and consent to it. The idea seemed a bit weird to me at first since I can only imagine myself with 1 person. But it's good to understand that some people can love more than 1 person. And as long as everyone in a poly relationship has informed consent, that relationship is pretty healthy.
It's disgusting. Can you really be normal friend with someone you've had sex with? I mean come on, I can imagine one of them going to the other if they fought and have comfort sex. I honestly think when having a relationship, you should cut ties with those sex friends. I mean "were not doing it anymore" and "it's all in the past" doesn't really reassure a person.