Eclipseranch, Didi has passed away.
Barry, I've been in your shoes. A couple of times actually. The first horse I ever lost was a spirited Arabian gelding. When he got into his early 20's he would have episodes of being very quiet when I rode him (not his style!) and I put it down to his age and him finally settling down.
Then he would lay down sometimes (more than he used to) and I didn't know what to make of it because when he got back up he seemed normal and ate normal. Just his age catching up with him, right?
Then he would go off his feed from time to time but be eating again in a few hours. He would seem to colic and pull right back out of it.
Long story short he finally had a major episode of colic that he never recovered from despite vet care. He was 24 yrs old. One of the toughest things about it was it wasn't a "rolling thrashing have to make a decision right now" type of colic. It was more like he quit eating and started to waste away.
I am not a wealthy owner and he was not insured. He was a backyard trail horse. So after trying non-surgical treatment for about a week I finally admitted defeat and had him euthanized. I have since lost two more horses but I think the first one was the hardest. Looking back I could see the symptoms coming on for a couple of years. Just him slowing down out on the trail was a sign something wasn't right and I told myself it was maturity catching up with him.
So we all second guess ourselves and feel guilty that we didn't read the horse's signs sooner, or misinterpreted them. But I don't think it would have changed the outcome in Bel's or Didi's case. Both Didi and Bel had something majorly wrong with them and we had good intentions. I know I flubbed up, but what can I do about it? In hindsight, I think he must have had an entrolith or cancer in his intestines.
We all misread the horse but a good owner tries their best to get to the bottom of it, and you certainly did better than the majority of horse owners out there in trying to get to the root of Didi's troubles. You went above and beyond in fact. Many people just call it bad behavior or in my case, old age, before we realize there is even an illness going on. The best we can do is try to learn from the experience and be more aware if we are ever in the same situation again.