Can the mother of my child legally move three hours away from the father? If so, how can the father fight this from happening?

The mother of my 2 year old child currently lives 45 minutes away from my residence in another state. We have an agreement we both signed and went through a court in Ohio. She has custody and we have a visitation agreement that give me at least 2 specific days of the week to see my child. My ex very recently started dating a guy who lives 3 hours away. After a couple dates she is talking about moving my child away so she can be with him. I feel she is not looking out for the best interest of our child in even considering this move. His entire family, mine and hers, live within an hour drive of each other and he sees myself and his grandparents several times a week to give his mother coverage to work. This move would basically pull him from everything he knows and everyone he loves and who loves him to move him to a new area where he will have to be transport 3 hours to see his father and family he has grown up with. I am considering seeing custody of my child.