I am divorced and my son left this summer to visit his father in a different state, now he doesnt want to send him back

We have nothing in the divorce papers stating who would have custody, it was verbally agreed my son would live with me..because i filed for child support, and possibly he has not gone through his military command with handling it, instead of owing me back money he wants to keep our son...he is using the excuse that i am unemployed and recently i moved in with a friend out of state to get my son away from a bad situation, he has been living with me the last 5 years now where i was his custodial parent and caregiver...i have texts stating he would have him back to me end of this month..i am currently residing in PA and my ex is in TN, what can i do?