My husband has a 14 yr old who for the last yr has resided with us in Maine, My j=husband still pays child support on an order put in place in Massachusetts. He is now looking to gain full physical custody and stop the support order, in what state would he have to go through for this

Massachusetts.

The courts of that state have exclusive jurisdiction over custody, unless neither the child nor the other parent still love there. Despite the fact that, last I checked, Massachusetts is the only state which has not adopted the UCCJEA, it's law on the subject is substantially similar.

And if he wants to change the support order, he would have to ask the court (in Massachusetts, as I understand) which originally entered the order.