I'm going to freak out on my girlfriend for asking if she can talk to her ex
Freaking out sounds extreme. Why do you feel you have do this?
Yes, because of me making it a habit to freak out on everyone.
Talking to her ex might mean something is still going on with them, you have every right to be jealous. Calmly let her know that you are not comfortable with her being friends with her ex anymore and that's all there is to it. Freaking out makes everyone detest you after awhile, it is not a pleasant way to communicate.
I'm going to be aggressive and prove myself as the boss of her actions.
Blowing up at her will make things more tense. If you keep your cool you will look more mature and trustworthy to those you care about.