I'm going to break up with my girlfriend because she's not allowing me to have contact with an ex
Is she just trying to stop you from being friend's with this ex-girlfriend of yours?
No.  She knows that I still love me ex from before.
If you still love your ex and your current girlfriend knows that, it's understandable that she doesn't want you to talk to your ex any longer.
She is not making this easy. How am I supposed to just dump someone that I thought was my future wife.
It sounds like you two need to sit down and talk about your feelings. I think your girlfriend feels like you don't love her and want your ex back.