I am really glad you didn't get seriously hurt. Getting thrown from a horse can result in so many serious injuries (broken neck, dislocated discs in your back, etc etc).
Training a horse from the ground sounds like this is above your current skill level. He was very clearly giving you WAVING RED FLAGS that something was different about his attitude. The fact that you failed to see these obvious cues makes me agree with the others that a trainer (in person) will greatly help you with this horse.
Don't take that as slam against you -- ALL OF US were where you were, at some point in our lives. You have to start somewhere.
The only thing is, I feel I did a great job on his ground work. I have completed everything I have read about online regarding groundwork, (most of it on this forum) and watched in training videos and had advice from people at my barn. I put A LOT of time and work into it and I feel it is very good. When I rode him for the first time, at my barn, he didn't think twice about having me on his back...or the next 4 times I rode him so that is why I am confused as to why yesterday he decided he didn't want me riding him...
I agree I should have listened to what he was telling me, but I felt if he kept walking circles around the mounting block he was getting was he was wanting as well, me not riding him. I planned on just sitting on him for a second and hopping off because he was so antsy, and if I sat on him for a second he still wouldn't win the battle at the mounting block...but he had a different idea.
Riding 5 times in the past 2 weeks typically is NOT enough for a very young horse just starting out. Short daily sessions are much better.
How are his ground manners? Of course, on this particular day, they were horrible, since he completely refused to stand still. That's why moving his feet, making him lunge, and making him LISTEN and FOCUS on you would have been more effective before you got on. As someone else already mentioned, that's a "flight check" to see how your horse is feeling for the day.
Before I get on a young horse learning to ride, I'm paying attention to their behavior the instant I get them in the pasture. How do they stand when I check and pickout all of their feet? Brushing them? Saddling? Then I will lunge them for a few minutes to make sure they stop when I ask, turn when I ask, back up when I ask, move their shoulders or hindquarters independently when I ask, etc. Then I will stand next to them on the ground, and ask them to them to flex their head (with the bit) both ways so I know that my "turning" and "stopping" will work when I get on board them. If they have been acting goosey, I will ask them to give their head to my knee as I am mounting. That way, if they do try something, I've already got their head to my knee to stop the buck.
Depending on the horse, I will eventually skip some of these steps. But with some of them, I'm doing this check for a full 30 days. Just depends on the horse.
If you are not able to ride through a buck, it's best to have someone else ride. You don't want your horse getting away with it.
Or, if you can at least keep a hold on the reins when you have fallen (this is why I ride young horses with long split reins), then you can work their BUTT off immediately from the ground, and show them that this was NOT acceptable.
I'd be very careful with your horse right now, because he got you off once. He has now learned that he can do what he wants if he gets rid of you. It will be a hard lesson to re-teach for him.