it still looks to me that the big problem is eating. I always thought you had only as many miles in your legs as your conditioning would allow. But what I've found is that as long as I eat, I can keep going. And if I do get to a very low state, I can eat and get back to a reasonable level of performance. I find that candy helps in those cases. The issue of not being able to eat after I fell behind in my calorie intake has happened to me a couple of times, mostly when it's very hot. In those cases it can get tricky, but I've always managed to recover by, get this, eating.
I'm a proponent of not riding too much. Too easy to get burned out. I used to get over-trained in my youth. That's not likely to happen now, but the desire to go ride has to be there. Short, faster rides are the way to go. However, the OP needs to convince himself that he can finish a long ride. It certainly is a lot harder to do something when you are convinced you aren't going to make it.