I want to know what has and has not worked for you guys and maybe even how you should have, would have done it looking back now. Thank you for any advice you can offer. Personally I would say nothing to the N about their illness. Divorce happens all the time simply for irreconcilable differences. Anything you tell him will be twisted back onto you.
Divorce is a legal disconnection.
You can tell him, or not, that he's a N after you have reached legal safety. A Wall of Pleasant is the best all around. It allows both of you to go on with your lives separately with dignity. The fact that he's away is an excellent opportunity to leave peacefully. Decide to leave and make your move legally, quietly and with as little drama as possible.