Living abroad with my child

I have a 3yrd child with my ex husband and i am looking to move abroad to Europe with my child. My ex husband has told me he will fight me all the way to stop me from going. We have joint custody of my child but he lives with me. My ex does not have set days he sees him and sometimes goes 6 weeks without seeing him. I would like to know if he can stop me and my child going and if he does how do i go about detesting this.