You might reply by simply asking "Oh really? What kind of changes?"

BUT - you must be ready to rein in your expectations and prepare for answers you won't like.

- yes, he might fulfill your wildest dream and say the "good" change has been getting rid of OW. I'm not betting on that one, but it's possible.

- the "good" change might simply be something work- or domicile-related, a move of some sort

- or the "good" news might be that OW is pregnant with his child, or that they're getting married. Brace yourself for that possibility if you ask.