Correct God is not bound to continue your existing...
ie could have chosen differently
Correct God is free to determine you no longer exist...
No this does not follow. Nothing can exist or
continue to exist apart from God Determining its next moment of existence.
This does not mean God is bound to continue your existence. God is free to choose that you no longer continue to exist...
... If God didn't have to be bound then...
God is free to withdraw his sustaining power at any moment.
The part that you can not grasp is the fact that if God determines to stop exerting power over you, you don't continue to exist by an
independent power, in fact you no longer exist at all.
You assume that if God stopped exerting power over you, you could continue to exist and be doing something else but this is not the case.
You exist therefore God controls you.
...why was He unable to give us unbound libertarian choice?
Because, according to scripture, apart from God there is no other determinative power in existence that can continue your living, moving, and being.
It's a logical impossibility that is contrary to scripture.
...