If you are asked to give information, and you know there’s a problem that can have a negative impact on a marriage, tell the person inquiring you’ll get back to them shortly, and call your Rav. If you know in advance you might be called, even better- you can ask the shayla ahead of time.
You’ll be asked by the Rav to describe the problem to him, tell him how you know about it, and other details.
Then, simply do as you’re told.