It's NOT defiance. A horse that doesn't trust the rider CAN'T listen. He can't willingly follow a leader that isn't being consistent. Sorry, but that's what I'm reading here. I''m not trying to be rude, but I think you need a real trainer.
There are things that people can do on their own, problems they can fix, and then there's problems that aren't going to go away but get worse (already sounds like that) unless a pro takes over in person.
I don't think your skill level is good enough to treat this problem. I think your best bet is to find a good trainer you can trust and have the trainer retrain the horse to not resent being asked to go forward....rebuild that go forward cue....because, frankly, you lost it somewhere.
And you're not going to get it back by how you're going about it. Not by yourself. You're just going to get hurt or get the horse hurt. So...please find a trainer who can fix this...AND then that same trainer can train you as to how to apply the cues correctly.
If it's not pain then it's simply, this horse has lost a go forward cue. And a horse that has no go forward cue will rear, buck, etc... and will be so called "buddy sour" which is just another word for: "horse that don't trust rider"
Get a pro to help you. After all, you've got horses to have fun, not to see how many frequent flyer miles you can wrack up with each buck or rearing up....
A good trainer (not an abusive one, nor one that's just going to smack the horse in the butt)....who can retrain the horse to be willing and to retrain a leg cue on him....is a lot less expensive than the ICU.
Please get help.