Okay so I get not talking to your spouse about R or M but what if they are the ones to start a conversation about it? How do you respond? Do you talk or say I'm not talking about this now?
You just want to validate (acknowledge) what they are saying. Doesn't mean that you agree, but you have to let them know you hear what they are saying and you understand their point of view.
You have to be real careful not to let the conversation progress into an argumentative state. Try to keep your emotions in check no matter how much he tries to re-write your history together or paint you in a bad light. Steer the conversation in another direction if that starts to happen.
"It is curious that physical courage should be so common in the world and moral courage so rare." -Mark Twain
