If you ruled out pain with the vet…I’d send him to a PRO. Not a cowboy per se but just a good professional trainer. If you are going to show him, send him to someone who will get him out and competing a bit for you and who has experience with OTTBs and green horses.
After as bad of a fall as you had…any normal person will have some nerves. To me he sounds like a lovely horse who is sensitive. And a horse like that will sense your nerves and may be more likely to overreact. The only reason I may consider more of a cowboy, is that I know of a really good one who is great at working calming through these issues. And it sounds like this may be a horse who needs some training in not over reacting to something being not in perfect balance on him. I don’t want to say, desensitivity training…as you want them to be sensitive, but you just don’t want the reaction of the broco you got. Especially not since you have been hurt. I would suprised if he couldn’t be trained given the right time and with the right person.
And just basically, he needs his confidence built up by a rider who doesn’t have the baggage. I doubt it will take too long, but let a good pro get him over this and put some miles on him in more atmosphere so you can be confident in him as well.