I know ME by the CFS name, my husband has had it for three years now. He can't get to the end of our road without collasping and barely lasts the day around the house, although he puts a brave face on it.
The garden must be both a source of healing and exhaustion for you Sam. The fact that you can actually complete a gardening job, however small, is an incredible achievement with this condition, I can't imagine the frustrations you must suffer.
My husband sit with me sometimes, he's not an invalid and has surprised me with some monir landscaping before now but as you might well know, its the sort of activity that will put him in incredible pain and fatigue for days after.
I keep telling him not to but its the only way he stays sane. I think the day he admits defeat, will be the end of his incredible spirit. I admire his determination to win.
All the best Sam