Georgia child custody laws, procedure for modifying child custody

Child Custody Modification: My son is 8yrs old. I have 100% primary custody and 50% legal with father. However, my ex-husband wants me to agree to allow him to spend addtional time with him. He gets my son the 1,3,5 weekends of the month in addititon to every tues for a couple of hours every other week after school. My son is enrolled in boys scout and addtional activities that his father is not actively involved. Also, my son has been doing things I believe come along with growing pains. He is not a unruly child but doing things like being sassy and acting out of order. He is not a child endanger of going to juvenille. My ex-husband is certain that he needs him. My position is the fact he does not utilize the time he already has. I am good mother I own a home, employed,have 2 degrees and make sure my son is provided for in all ways. I am not an unfit parent but my ex thinks I am not able to provide what he can. Does he have case against to modify child custody because he feels can have more of an impact on him? - Is this your question? Add additional information