Here's what I see from what you described: you're about 17-18 years old, and you have your very first horse. You have an Arab, you picked a very sensitive and intelligent breed as a first time horse owner, and a youngster at that.
Regardless of perceived errors or mistakes made, and circumstances which were beyond your control with his past abuse, if you have given your word to the horse to care for him for life, that is a rare and special commitment few horse owners will make, and I want to say how much I appreciate your dedication. I appreciate that you were compassionate and took a horse in that may have otherwise been sent to slaughter.
I hope the new barn friends you've made will help give you and your horse the confidence and learning tools that will work for you. The two of you are young, and you can learn and grow together in untold ways. Everyone has opinions, and you may be overwhelmed with different perspectives, techniques, attitudes, training tips, etc. Just pay attention to your horse and what works for him. It sounds like you know him better than you think you do, and it's just a matter of finding the right environment and people to give you both a hand up.
Horses mirror us, for better or worse LOL, and we are all learning about ourselves and our horses no matter where we are in our journey. I'm an old bat and I still screw up LOL. I don't believe anything is impossible.
If for any reason you should decide that he will be a better match for someone, you can protect him by lifetime leasing him with a very explicit and detailed free lease contract, rather than selling him. If that is something you feel is right.