Willow,
I don't use the word "no". I do, however, delay or negotiate with the tweedles. And having said that, they are a good deal younger than your difficult child - would he see through it?
Anyway, using that strategy has saved countless hours in rages & meltdown; countless tears shed & crisis calls. I just don't use the word "no".
I'm sorry you're feeling so down about difficult child - we all get in that position. We all look at our children & wonder. We are all brought to our knees at one time or another over the choices or some antic our difficult children bring into our lives.
Time to find a good book or some other fantasy place for the time being. Just let it go for tonight. Get some rest.