Emancipation or Guardianship for My 16 Year Old Stepson

My question involves emancipation laws for the State of: Arkansas and Missouri

My 16 year old step son who has lived with me and his mom for 5 years (we are married) wants to move from our home in Arkansas to live with his grandmother (my wife's mom) in Missouri, where we lived formerly.

My wife has joint custody with the father, who lives close to where he would be moving in Missouri, although the father and son do not want to have any relationship with each other.

He has a girlfriend there and is hell-bent on being close to her. What do I and his mom have to do to enable this? Mom doesn't want to him do it, and I won't do it unless I have guarantees that I will not be financially or legally responsible for him ever again (particularly should he get his girlfriend pregnant).

What is the law?

The law is that you are legally and financially responsible for him until he turns 18 unless he is legally emancipated, and he won't be legally emancipated on the basis you suggest.

For a judge to approve a petition for emancipation, he would have to have the means to be completely self-supporting (no being financed by mom, dad, granddad, Aunt Susan, or the state) and have a reason that is a hell of a lot better than "I don't want to leave my girlfriend".