Let me start by saying this... I too have been diagnosised with ADHD & Bi Polar, I am 39 years old. My son is 14 1/2 years old and also has ADHD, obssesive compulsive disorder, and (not diagnosised) but possibly bi polar. I don't know the current age of your son, but... we have raised our son that he can't use any of these things as a disability. He must use the his medication as a tool, and work with it, not use it as an excuse for bad behavior. We have dealt with this since he was in the "terrible 2's, God awful 3's, and the hell a' shis 4's". We have consentrated on consistant disipline. A lot of parents don't have consistant disipline tactics.
I have a good friend who once told me that taking your children to mental institutions, and psyciatrists often times has the oppisite effects than the desired results. He said you have to be very careful when dealing with a childs mind because they may just be going through normal behavior for their age, sex, family enviornment, but when you take them somewhere because you think they have a problem, then they begin to think they must have a problem, or they are a problem. This may totally be off base, and you may of had different circumstances for why you took your son, but I am sure there is more to the story than what was written above.
Have you thought of the possibility that your son feels like he is the reason you were considered an outsider? Have you thought of your sons feelings of how you, your husband, and the "new" baby "girl" are one unit and he will always be the "outsider"? He may feel like the "girl" gets special treatment. He may be acting out for your attention. It seems a lot of this happend at the same time, you having cancer, getting married, and his acting out? I have no doubt this as affected this child. How would you be reacting if the closest person in your life was considering putting you in a "long term facility"? A lot of times people think they know how someone feels about something, but it is really not that way at all. Children are known for saying what we want to here, not what they are really feeling. I am not makeing any comments to bash you at all! I am simply stating that the problem is deeper than ADHD and Bi Polar.
With good treatment, ie myself, and my son, a person can lead a perfectly normal life. My son is a freshman in high school, and has a GPA of 4.5, and is in honors classes. He has his faults, but for the most part he is pretty normal. He has the teenage mouth going on, and the we are dumb, he is smart. His room and bathroom just seem to stay a lot cleaner than the rest of the house.
As far as your husband goes, if he truly feels like this is his son, he would be offended that you even thought he wanted to be anywhere else. He seems to be a great guy, and signed up for the long haul. Imagine how my poor husband feels, a "crazy" wife, and a "crazy" son. He has stuck with us and been around for 18 years. (Plus 5 years of dating prior to the 18 years) He says he wouldn't be anywhere else.
This may not have helped at all, but maybe you will be able to get something from it.
Good Luck!