Is there a court order in place? Does your son have visitation with his dad? If you did move and your ex wanted to keep you from moving back, he'd definitely have to go through court depending on if there was a court order already in place.
Yes there is. I have physical custody and we share legal custody, he visits his dad in the summer and spring break. So DS's residence is in my state. However I would assume that if I moved closer then wanted to move further again ex could fight me on moving further away?
It depends on what the court order says. If it says you determine geographic location of the child then you choose where he lives and if you want to move back or further away then you'd be able to. He would be able to take you to court if he wanted that changed, but you'd probably be moved by then, so there would be no point. Like right now he can take you to court and say that he wants his son to live over there with him instead of you, but he hasn't.