Susan,
You really sound strong here. I am very impressed. What you are doing is so hard, yet you and husband are working together and doing what is best for your son.
Be sure to take time to acknowledge the broken heart that I know you must have. Be good to yourself and husband. Maybe make a date night, or a nice evening at home with no talk about difficult child (sort of an "at home" date). Give yourself a bubble bath and a manicure or pedicure, whatever relaxes you and makes you feel good. REad that book you have been wanting to, or get a totally decadent dessert or box of chocolates to indulge yourself.
You really have come a long way (but no Virginia slims!) and deserve a pat on the back.