Ah, the OPP (one penis policy). It's one of my favorites in the world of non-monogamy: "you can sleep with other people, but not other guys (regardless of whether you're attracted to the same sex or not)." Honestly, this is a really crappy situation, and I'm sorry you're in it. It sounds like he wants the benefit of being with anyone he wants to be with without allowing you the same courtesy out of a sense of possessiveness; he doesn't want to be "tethered," but he wants you to be, and that's simply not fair.

Based on what you've said it sounds like this isn't really something you want. Maybe you said you did at the beginning, but there was certainly muddy communication about the logistics (asking that girl on a date for the two of you without asking you first was not okay), and it certainly wasn't made better between that and talking about how hot your friend is all the time. I can see why that would bother you; it's upsetting, and you shouldn't have to put up with it. You should be with a guy who cares about your thoughts and feels and isn't just trying to fulfill his own fantasies, and it sounds like that might be what's happening here.

It's up to you whether you stay or not, like others have said, but if you do you need to be very clear about your boundaries, what you need to feel safe and valued, and if he steps on them, either don't be afraid to point it out or, if he does it repeatedly, leave. There are so many other guys out there and you deserve better. You don't deserve to come in second, and you don't deserve to be taken for granted.

Good luck and PM me if you need anything else.