I am very sorry for your loss. This is not your fault so don't blame yourself. You tried to figure out what was wrong and I can tell that you loved and took good care of your bun.
I have a spayed mini lop that just turned 1 year old. I used to keep her in a large exercise pen but the sound of the cage rattling at night drove me nuts so I began free roaming her in my bedroom. She became more laid back and hasn't been too destructive after bunny proofing (covering the wires...