How about this, hd (your tone throughout should be very cool and kind, no matter what she says):
W: (after I roll over after being rebuffed), See? You just need to learn to be comfortable with me saying "no."
H: I know exactly when I'll be comfortable with you saying no.
W: When is that?
H: When I have stopped loving you and no longer care whether this marriage survives.
W: Oh, so now you're threatening me!
H: I wish I were threatening you. Unfortunately, what I'm doing is issuing a prediction.
W: Well, if you feel that way, why don't we just get a divorce?
H: Because I'm not there yet. I do still love you and I do still want our marriage to survive.
W: All you care about is sex. You'd break up this marriage because I won't have sex with you every time you want!
H: I'm not going to discuss this with you. But I assure you, one day I will cease to care whether we ever ML again. One that day, whether or not we ever divorce, our marriage will be dead, and there will be no going back. Watch me carefully, and you will see the signs when it has happened.

Whatever she says after this, do not reply. If you can't be silent, just keep saying very kindly, "I'm sorry, but I've said all I have to say on the subject."