it seems not too uncommon to have not-so-happy endings for parents who adopt. I'm surprised there are no formal help groups. I hope you'll be able to find some comfort somewhere.
My former boss and his wife has two natural children but also adopted two First Nations siblings. They both had fetal alcohol syndrome and proved nothing but trouble. The girl ran away constantly, finally ended up pregnant and moved back to her native Saskatchewan when she was 17. Her brother became involved in drugs and alcohol and was physicially abusive to the family. He also moved back to Saskatchewan when he was about 17.
They were given all the same opportunities as their two natural children but I guess the nature proved stronger than nurture.
I also saw a program once on people who adopted children from foreign countries who have had nothing but trouble. There's even a "camp" for them where there is a woman who is a child-whisperer of sorts. She uses her farm to rehabilitate these children. They don't come back perfect by any means, and some never go back because the parents can't handle them anymore. It was quite startling.