Oh my stars... broken back.. are you ok?! I'm so sorry to hear about your ordeal. The timing is unfortunate, too - there are so many unwanted horses, even without behavioral issues, trying to find homes out there. It would be ideal if you could turn him over to a knowledgeable, experienced horse person - I know you're worried about his future, so perhaps you can put a buy-back/first right of refusal clause in writing?

I'm also sorry to hear about your deceitful trainer - seems like there are many of those out there.