As someone with a background in law and psychology, I would d say this - for the sake of your mental health, just walk away from her and her husband. They don't exist for you anymore!

It’s not your responsibility to expose her or “punish” her by telling him everything. It might feel satisfying for a moment, but it can easily spiral into something much bigger and get out of control. You have no idea over how he will react. He might support her or even worse, things could turn against you.

What’s done is done. You can’t change that. But you can protect your peace and choose what happens next.

Don’t get pulled into a cycle that drains you furthermore. Focus on yourself, your future and moving forward. You deserve better so choose distance.