You don't have to distance yourself from your son because of who he is, whether he can or can't make better choices. You can learn to accept him. That is what we have to do regarding anybody we are in a relationship with that we love. He was not born wired to be a top executive. He has been drug affected and had a traumatic brain injury, b ut he is still a person in his own right. If he abuses drugs, that is on him. But not being an executive was pretty much not going to happen and you must have realized this, in the back of your mind, when you heard his history.
You have to understand...you and your son are two very seperate people. Your son's triumphs are not yours. They belong to him. His failures are not yours. Same thing. In the case of adopted children, of which I have three, they do not even share our DNA so may be extremely different from us, but still worthy of our loving them as they are. I did realize this when I adopted. But I also went into it without lofty expectations too. You can change your expectations and this will lessen the pain. Yes, YOU can.
I was wondering if you were belittled, abused, made to feel horrible about yourself as a kid, like I was. The sooner we accept our childhoods and how it may be affecting us now, the easier it is for us to see our faulty thinking that stops ups from being happy.
Your quality of life should not depend on what your son does. The only person who can make you happy is you and whereve you go...well...there you are!!!!
You gave your son, as we all did, every opportunity to be what he wants to be or is capable of being and this is what he is doing right now. Accept it! You may want to google search "Radical Acceptance." It is an awesome concept 
