Wait, your trainer is unwilling to get on this horse, yet is telling you this? Like I said, I don’t judge her for her unwillingness to ride a horse that’s reared, but how can she tell you this when she doesn’t have this confidence herself? Especially after she found not one but two young horses when I assume she knew your history of injuries and lack of confidence.
If you don’t feel comfortable riding this horse, there is no obligation for you to keep him. I agree with others–he’s not the horse you need right now. From your description of him, even after training, he likely needs a program with a very brave trainer and a very brave rider with a sticky seat and quick reflexes. It’s really hard to reinforce the lessons of training if you’re always riding defensively, thinking what he’s capable of pulling. This doesn’t mean you’re a bad rider–but take some lessons on a boring schoolmaster who is beneath your level of difficulty, in terms of his personality, to remind yourself of what you can do.
Confidence is built by having mostly good rides, not scary ones beyond your level of ability to figure out challenges. Sometimes our fears are irrational, but sometimes they are rational. And even if you could overcome your fears, it’s also worth asking if this is still the best horse for you.