New and need custody help!

Hi< I am desperate. My son is almost 15 years old. He lived with me(I had custody) of him until he was 8 years old and I moved abroad. He did not want to live with me, so his father got custoday while I lived abroad, and as I worked on my husband immigration papers, we talked everyday and he visited me all summer long. I have been back in the states for almost 3 years now. We did not go back and change the custody paper when I moved, I couldnt afford it and m y son was fine with the arrangement. He lives with his dad mon-fri and is at my house on weekends and holidays. He has a brother at my house, and at his dads he doesnt have any siblings. He hates his stepmom, she verbally abuses him. He wants to now move in with me. Great, but his dad says no. His dad lives 12 miles away from me, so he is not that far. His dad told him he couldnt move in with me, no reason at all, I am not a bad mom, I am a stay at home mom, we live in a nice house, I cook from scratch, There is nothing bad about me. He told his dad last night that he is not going back there to his dads house. I dont know what to do. Am I going to be held in cotempt of court? My son wont go back, he is crying and very upset about not being able to live with me. Also, Iwent to a lawyer and it would cost $3000 and up to change custody, I cannot afford that!! HELP!