You're in a R with this guy for the rest of your life so you'll have to communicate with him. Humor worked for me. I quit being so dad-blamed serious about everything and would be light and humorous as much as I could. I would be straight forward and matter-of-fact when that was called for. No P/A BS (I was a master)or emotional blackmail.
Being detached doesn't have to mean you never communicate, it's more about the emotions you detach from. Every interaction isn't charged. If you're not there yet, you're not there yet.
State your boundary here as you see it.
Me 57/H 58 M36 S 2.5yrs R 12/13
Let me give up the need to know why things happen as they do. I will never know and constant wondering is constant suffering. Caroline Myss