It's not fair, but no one ever said life is.
Now that we've established that, what are you going to do about it? You can't sit around and wait for other people to change. Their insecurities and rules aren't likely to go away, especially overnight, and meanwhile you're wasting time and energy on them when you could be spending it meeting new people.
If polyamory is just something you're trying out, then you don't need to be hung-up on one particular arrangement. You can date singles, have different relationship styles, whatever you want. There are plenty of opportunities if you take the time to find them, and seize them when they come up.
Even if you value their company and you don't want to break up, you don't need to have all your eggs in their basket, so to speak. You can continue dating them while pursuing other options. Honestly and upfront, of course.
I don't need labels to define me. They're sticky and I hate the glue they leave behind.