... After all that hard work I did to make her the trail horse she is, I now have to start ALL OVER! Doesnt life rock?
What you need to realize is that this buddy sour problem was never preperly addressed properly in the training. You have a "hole" in the training, which doesn't invalidate any other training.
You just need to fix this hole.
And yes, your friend was wrong for leaving you like that. But remember, you can only take responsibility for your horse's training, never for what others may or may not do on trail. There will _always_ be someone else running off, taking lunch out of a plastic bag, flapping a raincoat, screaming at a spider... whatever. I have learned to accept others shortcomings as inevitable and do what I can to account for it in my horse's training. When the manure hits the fan, I would rather be safe than blame someone else for my injuries.