I agree with Karen that his wanting to be with his friends over being with you is normal....BUT this is not a normal situation and he is not a easy child.
Sounds to me like he is still ruling the roost and you are allowing him to do it.
Good for him for staying clean but why risk the temptation? He's now going from 24/7 supervision in the group home/Residential Treatment Center (RTC) to coming home and being allowed complete freedom again once he's away from you guys. Heck, I'd want to come home and would do/say whatever it took to be able to.
Maybe I don't understand the purpose of his coming home right now---or perhaps your goals are very different from what ours were? For us, our son's home visits were to develop/re-establish family relationships and trust, not give him the chance to go elsewhere.
Suz