Ok...I guess this isn’t really an advice site as much as it is a bunch of judgmental folks that think they are better than everyone. Oh well.
I wasn't being judgemental, I was trying to help you understand that parents are just as accountable to their biological children as they are to their adopted children. Not more, not less, but exactly the same.
If your wife gave birth to a biological child who appeared to have little or no problems at birth, and who then much later developed behavioural problems, would you be trying to return this child to God or whoever because you weren't warned about these upcoming behavioural problems at the time the child was born?
Regarding the adoption agency not telling you about these problems at the time of the adoption, if you can prove that the agency knew all along about these problems and wilfully neglected to inform you about them before you made the decision to adopt this child, then you may have a case for suing the agency for whatever money you might have to spend to help this boy overcome his problems. But you'll still have to keep the boy.
Finally, I suspect that this boy's behavioural issues may be caused or at least exacerbated by a bad and uncaring homelife before you came along and rescued him. What do you think's going to happen to his emotional state if you give up on him now? And do you really want to carry around the guilt for that the rest of your life?