Oh, man, I've lost it more times than I can count, and I know I don't have enough fingers
I think over time we figure out what is going to work for us, and put a plan in place, and try to make it work so that life with our difficult child's is easier.
I like TM's suggestions, and Linda's, and do think you need to put a game plan into place. You definitely need to lower your expectations for now. I completely understand your desire to have your difficult child "normal". I can tell you that I grew up one way (very strict parents, I never ever did ANYTHING wrong, and if I did, my father was coming after me with a belt and I never did it again) and my children are growing up another.
My difficult child 1, Dylan, he was a challenge for me. He was completely out of control, marked "severe ODD" by the old psychiatrist, and did not listen to ANYTHING. Every task that was asked, there was a fight.
I started small, with little things, and gradually worked up. We did this with behavioral modification, Wrap Around services, things like charts, rewards, etc. It took me almost 3 years total. I know, sounds like alot, but you know, the behaviors don't get bad in a week. You can't change them in a week.
So, many years later, my son is no longer ODD. I have no issues with him at all, it's almost miraculous. But, it took alot of time, alot of work and alot of patience. It wasn't easy.
Also took the right diagnosis and the right medications. Have to add that, too.
Janna