First off, so sorry for what happend to you, it happens to the best of us. My first word of advice that I would offer for the spooking is usually a simple fix. I have done this to all of my horses and they do not budge for anything. It's called desensitizing your horse. Start with something small, maybe a plastic bag, and approach the horse let him/her smell it and retreat the bag if he/she gets spooked; do not push the horse with its fear. Repeat until the horse no longer spooks with the bag in that manner. Then attach to end of whip and make noises with it, wave it around, etc until no longer spook again stop when spooked, eventually work your way up to rubbing it all over his/her body while attached to whip. Start small and work your way up with objects, he will learn that everything isn't a big monster that's going to eat him.
Also, if you do not want to completely desensitize to everything that you may come in contact with in the arena or trail, you can always start with the bike. Note: Always keep slack in the rope and never pull and tug on it to try to calm the horse down= turns into a fight. Lead your horse up to the bike while it is off until and basically repeat the steps as I explained with the plastic bag, allow him/her to know that the bike is harmless. This could take several minutes to hours/days. Always desensitize on the ground first rather than in the saddle. Repeat with someone starting the bike, keep the horse a distance from the bike, and do the same while the bike rides around the vicinity of the horse. Put the 'threat' there, take it away, put it there, take it away. Allows them to understand " hey there's nothing to worry about". When, and ONLY when, he/she is completely comfortable on the lead rope with the bike off, running, or idling, get on the horse and try slowly riding up to the bike until calm. The horse may be hesitant since you are not by their side anymore, but be patient. For the running or idling motorcycle, the horse may bolt( I can recommend a method for controlling a horse if it bolts or get out of control if you are interested, just message me.) Try to keep it under control. Basically keep working with your horse until you feel comfortable.
For your confidence, I really and truly think that the ground work for the motorcycle, plastic bag, etc will really bring back your confidence. As for getting back on the horse, which I have had to do many times. Get on the horse, and sit there, pet it, love it. If you feel nervous when you get on depending on if you can get your anxiety under control or not, continue to sit there and breathe deep several times, but if anxiety is too high, get off and get on once your heart starts racing. Other ground work exercises help a LOT with mutual respect and trust between you and your horse. Best of luck!