As one involved with adopted kids many times over, this is directly related to the shock of findig out that the life he thought he had and the parents he thought gave birth to him are in fact....all not true. And on top of that (and all adopted kids feel abandonment on various levels) he did not need to know right now that his mother left him for a man. This is a trauma. I would not be shocked if he tried to find birthmother for an explanation. In the internet age, it is not hard to find birth relatives....Goneboy found all of his just on Facebook and flew out to meet them in Asia. My other adopted kids have not tried, although they have my blessing. I think they ferl it will hurt me and eill not do it until I am gone. And I think they will easily find them.
At any rate, this is different from a child going wayward due to peer pressure or school trouble or even mental illness. This is a life turned upside down. Nobody is perfect, and condeming does no good. But righting a wrong is honorable and this confused child deserves extreme treatment before the drugs and other stuff kick in. Traumatized kids do have problems, even if they keep them deep inside until they erupt, and this kid is already coming apart. Apparently it is quite bad and followed learning about his truth.
This kid is going to need a lot of therapy to help him feel whole again. His entire identity was eroded. With no blame attached, he still needs therapy. This is not an issue to ignore or to expect to go away.
It will not. This is trauma, not Conduct Disorder. The origin is clear. Friends who have not adopted have not a clue.
Please get this child the help he needs and deserves. Maybe you need family therapy too. This is a family issue. But the boy also needs private therapy.