Out of state visitation for a disabled child...?

I have a 10 year old son who has cerebral palsy, seizures, learning/mental/physical disabilities, etc. His dad and I divorced about 4 yrs ago after I found out he was having an affair. His dad then left for 1 1/2 years without a word or any type of contact w our son. After a yr and a half, he started seeing our son again. One over night a week. (This was his decision, not mine.) I do have sole custody, with "reasonable visitation" per court orders when we divorced. Anyway, he is now planning to move to S.C (from AZ) at the end of June. He wants our son for at least 3 1/2 weeks during the summer. I am SO worried about my sons mental well being during the seperation. He thrives on a set schedule. Has had the same one, with the same people and environment for four years. I know he will be safe with my ex but I am truely worried about his stability Does my ex stand a chance at winning visitation thru the courts? What about my sons therapy and special needs day care here? I am so scared and so worried. Doesnt my ex have to notify the courts anyway? How much of a notice? Anyone have any advice??