oanh,
Finally had some time to read what you've written. You certainly have lots of "garbage" going on!!! I can relate to some of what you're saying. I'm going to throw in my two cents, take whatever you want, toss the rest.
You have two separate issues that both need addressing in order for positive change to occur. First, in order for you to effectively be able to help your difficult child, you and your husband need to be on the same page as far as parenting goes. As long as your difficult child sees your husband acting passive aggressively towards you while seeing his father act as the "good guy," the one who "fixes" things for him, your difficult child will not respect you, will not see you as an effective role model no matter how hard you try.
While I was going through the worst times, my husband, (definitely no "D" in front of the "H" then!) couldn't stand the constant "meltdowns," tension, stress, in our household. He effectively shut down, always taking the easy way out, preferring to give into the demands of our children in order to have a bit of peace and quiet, never stopping to think about the consequences of this. He refused to believe that our oldest, difficult child 1 had issues (looking back I just think it broke his heart too much at the time), and as a result, blamed me for just about everything that happened that caused difficult child 1 to explode.
It wasn't until quite some time later, after difficult child 1 was hospitalized, finished three weeks of outpatient daily therapy, was finally back in school, when husband and I attended counseling sessions with him, that we were fortunate enough that difficult child 1's therapist saw what was happening. He was able to make husband realize that it wasn't my parenting that was the problem, it was his lack of respect for me, that difficult child 1 saw on a constant basis, the inconsistent parenting styles, husband's always doing anything to avoid confrontation with difficult child 1, that was causing the most problems in our household, making effective positive changes impossible. Once husband realized this, and husband and I began following difficult child 1's therapist's advice, life with difficult child 1 gradually improved. husband and I gradually grew closer together again, able to forgive each other and move forward. Of course, this is a super simplified version of what really happened! Still, I can't stress enough that you and your H need to both agree to counseling, following the advice given, parenting as a unit rather than as two separate entities.
Parenting as two separate entities gives your difficult child too much power. At this moment, your difficult child has no reason to change his behaviors. He probably sees you as the problem. After hearing your husband constantly undermine your parenting decisions in favor of what your difficult child probably wants to happen, he has no real reason to listen to anything you tell him. This creates a vicious cycle. difficult child does something that needs to be addressed, you address it, husband disagrees in front of difficult child, husband helps difficult child, you look like the "bad guy," while husband comes across as the "good guy," etc., etc., etc...
When I was going through the darkest times, I used to think that there was no way I could raise my difficult children alone and felt helpless, powerless to change my situation, get out of what at the time, I believed was a marriage that should end in divorce. I fooled myself into thinking that husband and I could raise our children, then I could divorce later, have a happy life. WRONG! The bottom line is you need to work on your relationship with your husband now. If this is impossible, you need to either separate temporarily or permanently. I really wish I had understood this back then!
The second issue is finding the best possible help for difficult child. Others have already given you some excellent advice, and from reading what you wrote, I believe you will make this happen. Once you have the tools you need - The appropriate interventions and consistency, your difficult child will have what he needs in order to have the best possible chance of becoming a happy, productive, independent (with or without supports in place), contributing member of society.
Thinking of you today... Hugs... SFR
P.S. I hope what I've written doesn't sound too harsh. No matter what you decide is right for you, I'm behind you. Obviously, I don't "know" you very well. Plus, I know my personal experiences have lots to do with my feelings. This is just my two cents. Take what you want, leave the rest...