I responded in your other thread about spooking - he does not respect you as his leader. Therefore he needs to step up to the job and react to everything, because in his mind you are not capeable of saving him or making decisions for the team.
Get yourself a trainer. You could not find a more worthwhile investment of your time and money right now. You need to learn how to work a horse on the ground, you need to know how to time your reactions perfectly, don't give him an inch, but don't make him feel like you're beating him up on the time either. Your reactions needs to be appropriate to his actions, does his little leap sideways need you to run at him like a screaming banshee, or quietly correct him by moving him back over?
A trainer will help you with this. On your own, a bunch of people on the internet aren't there with you to tell you when and how to react, and when to back off. You need someone with you, helping you. We can only give advise, but that person standing next to you telling you what to do is the best thing you could possibly have.