Stop pretending that you know what he’s going through. Stop wanting to make him feel normal. Stop trying to keep him sane. Stop doing things to help.
You can’t. He knows it. You know it. You are fighting a battle that doesn’t need to be fought.
Love the parts of him that you consider busted. Accept the things that are not normal. Embrace the fact that a sane person could not do what he did and be what he is. Do the things that make him happy and not the things that are helpful.
He deserves to be who he is without giving up what he has become. Not everything that is broken needs to be fixed. Sometimes it’s better to love the mess rather than clean it up.