It sounds like you've done everything you're "supposed" to do.
Now comes the waiting to see how it all plays out.
You have to trust your boyfriend to handle his um, affairs like an adult.
Whenever there is a problem, speak up. Make sure you've identified the problem and are not focusing on "symptoms" such as jealousy.
Having said all that, it is possible that your "gut" feeling is telling you that this new lady is a cowgirl, and wants your boyfriend to dump his other relationships so she can have him for herself. If he is "really poly", then it won't work out for them long-term even if she gets what she wants. If he decided that she is so wonderful that he wants to be with her forever and is willing to make the sacrifice of discontinuing the practice of non-monogamy, then you can't really control that or put a stop to it, no matter what you do.