I'm going to get angry at my family for seeing my ex
Do you want to argue with them?
Definitely, my family is hurtful for this
While it may upset you that your family is still spending time with your ex, if you dictate who they can or can't speak with then they could become upset with you. Are you sure you want to potentially start a fight this large?
They know what I went through with him. They betrayed me.
It's horrible that they've made you feel that way! But, you still can't control who they spend time with. How about instead of arguing, you let them know that you are hurt and try to reason with them?