"I'm still not clear as to what Catie actually wants, whether she wants an open relationship"- Josh
"So I kinda need to know that" - also Josh. Are you kidding me!? It's very clear, Josh. She sat you down and had a whole conversation about whether she will be happy with "just" a monogamous relationship and that she fancies an open relationship when she marries. Not only that, but she has been SHOWING you what she wants with the constant need to make out with friends and strangers and having no qualms about whether she hurts you or not. She is actively cheating on you when she does this. So you are already in an open relationship whether you like it or not because you are putting up with this behavior. Catie told him straight up, "I like the chase," and that will not die down when she marries. Josh is a fool and deserves what he gets at this point.