It doesn't seem uncommon. Heck, even I was implicitly told I should feel free to see other women before I was even in a polyamorous relationship (I'm straight though, so tough luck!).
I think it's important for you to try and understand what your jealousy is telling you. You say you're angry, and apparently at the other guys. Are you feeling like they're praying on her? Like they will hurt her? Like they're trying to take something away from you?
I think if you manage to identify what exactly is causing these feelings, it will be easier to deal with them because you will be able to contrast them with facts.