The good thing about DBing is that you don't just get "one crack" at most of these things. As much as we make white-smocked rocket science out of it, the truth is that you really can't screw it up that bad in any individual encounter.
And most of the time, you have multiple opportunities to get a point across.
If you go dim or dark (and I suggest you do), believe me, your husband will ask you SEVERAL TIMES "what's wrong?" Although you shouldn't entertain him with an explanation or answer every single time, you will be able to tell him once or twice that "I DO care, but because of your decision to have an affair, I find I need to protect myself emotionally" (or some similar language, that's your words). Or "I do love you, and don't want a divorce, but I also need to be prepared to get on with my life because of what you're doing."
TRUST ME, he KNOWS that you love him. He just now has to know that you love and respect YOURSELF too much to allow him to treat you like this.
