Sorry you are having trouble - for me, the most helpful thing was to re-read my DS's neuro psych report - it highlights my DS's strengths and weaknesses -- that way I can remember the good and bad of his ADHD.
I am now reading The Self Driven Child which is helpful but more on the issue of techniques that help, but some on why brains work the way they do. I recommend it.
Also time helps and noticing what works and doesn't work for your particular kid. That helps more practically than just knowing things are hard for him....