Show, Here's another thought;
Is this the right horse for you?
I do NOT see the point of having a horse that scares you just because one day he may have some great potential for showing. In the meantime, you find each encounter with him to be so stressful that it hurts? It's normal to have some fear of horses. I venture to guess near about every rider has that. I have a low running amount all the time. But it's the kind that makes me aware and careful of horses, not so much that I feel sick with fear. When I feel that kind of fear, I know that this is not my country, so to speak.
Dealing with a horse that rears on the lunge line and runs into/over you on the ground . .. are things that you will need help with . You cannot magically overcome them on your own.
I would recommend you get a trainer to work with both of you. If you cannot get to a place where the fear is low, then I would consider selling him and looking for a horse that BUILDS confidence rather than tearing it down.
You would be amazed at how much better of a rider you would become if you have a horse that you can lead, physically and mentally. It's true that with help from a good teacher (who can teach humans too) you may learn how to step over the small line that keeps you below this horse in his eyes and go above him in the totem pole, but if you are only faking it, horses usually know. They are masters at telling when the feeling is not sincere.
Have you thought about seeking a horse that better fits your personality? There is no shame in this. I would not like a horse that makes me feel like I am always on the edge. Some folks like that excitement and challenge. No thank you. I want to have fun, not fear.