I rode with an experienced endurance rider today and learned a couple things that might be useful for you, too. :)
• NEVER tailgate, or worse, let your horse walk right up behind another and turn their head so they can move in closer. They could step on the horse in front of them and cause a serious injury. You should be able to at least see the hocks of the horse in front of you.
• Make your horse ride his own path. Let's say you're on a wide trail with another horse...ride next to and slightly behind/in front of that horse, on your own side of the trail. He is not allowed to try to move in behind the other horse. He needs to learn to find his own path. If he blindly follows the horse in front of him, he is likely to trip and more likely to get out of control and hurt.
Do you have an arena or enclosed area where you could work him? It sounds to me like you could benefit from some time practicing patterns, transitions, and general listening. Then you might find an experienced trail rider who could take you out and help you get your horse to pay more attention to you.
I hope that helps! Good luck with your boy.
PS: I take my mare out alone on 90% of our rides so she has learned to look to me for directions to the point where she doesn't care if her buddy is lagging or speeding ahead. However this might not be safe for you and your horse yet, so use your judgement.