Hun, its just a matter of show miles. He doesnt have a lot of experience, so he gets nervous. Its like if you were running in a track meet for the first time, im sure you would get antsy too and a little disobedient because of nerves. As for your horse freaking out when the other leaves, its like if your best friend left you in the scariest situation youve ever seen! (people running around that you don't know, paying no mind to you, new surroundings, you don't know anything that's happening, and the ONLY security and thing you know is your best friend, then that person leaves) Its important to keep calm and ride on. Ride whats under you, not whats normal. Try and slooowwwlllyyy separate the 2 "best buds" each show lengthen the time and treat him when he stays calm. It works, trust me. And as for the speed, like I said, ride whats under you. GO GET EM!
hope this helps