Can my ex adopt my child?

My ex boyfriend has raised my child since birth, even after we slipt up and married other people. My childs biological parent has not been in the picture at all since birth. My child has expressed the want for my ex to become his father legally and wants to carry his last name. Is this possible in the state of Tennessee? How can I go about getting this done? My child wants to surpirse my ex for Father's Day.