Am I right to feel threatened if she dates him? What do I do here?
I know that's not fun to feel, but it isn't a matter of your feelings being "right" or "wrong." You just FEEL them.
You don't do things you are not willing to do.
She said she would drop him in a second if, after a trial period, I still felt uneasy. But at this point I'm not sure if she would even listen to that, since she's acted about our agreement very lazily.
Don't blame ya for not trusting her to honor new agreement when she's not yet given enough time to honor previous agreement and keeps PUSHING boundaries even when you display discomfort. There is coming to compromise in a healthy way, and then there's pulling the rug out from under you and keep changing things on you whether things are painful for you or not.
You don't sound willing to entertain a "trial period" since you had the agreement in place to begin with. Are you willing to do this trial period thing?
You don't sound willing to stay in the relationship without the agreement. Are you willing to stay in the relationship WITHOUT the agreement she's not going to date the ex?
Where is your willingness at? What ARE you willing to do?
If you plan to stay and see -- could this help any?
If you plan to break up because it's more trouble than it is worth to you and just not a runner -- break up fast and clean. I know that stinks in the short term -- break ups are not known for being fun. But look out for your LONG TERM health and get you to the Healing Place ASAP. Don't drag out a break up. It helps nobody move on to the healing place to let it drag on.
Sometimes the choices in life are "this stinks. That stinks. Which stinks the least then?" You kinda have to answer it for yourself here. What you are willing to do and put up with, and what you are NOT willing to do and put up with.
Me? I am def not up for doing things I really do not want to do. That's not self respecting behavior.
I'm sorry you hurt. I hope you can sort yourself out and come to a decision that best serves your long term health and well being.