confidential letter made public

What is the name of your state? Ohio

I recently had a problem getting my step-son's girlfriend to stop sneaking into my house and sleeping with our son who was still in high school. My husband was away taking care of his parents. So it was up to me to address the issue. I had ask her (nicely) on 4 separate occasions to refrain from sneaking in and staying. We have a security lock that requires a combination but every time we changed it he gave it to her. I finally called the girls mom and told her I needed some help with her. However, it did no good. The girl was still in my home staying the night without my permission. Finally I had enough when I found out she was accessing personal information out of my computer. I kicked them out. The girls mother calls upset with me and my husband and ask us to return her call. However, I couldn't reach her so I wrote her a letter explaining why she was removed my house.
This letter was marked confidential!

In the letter I explained why we did not agree with the immoral
behavior of the EX WIFE. We explained that she was a toxic parent and we resented how this effected my husbands kids.

So the Girls mother gives a copy of my letter to the ex and now THE EX tries to sue me for calling her a toxic parent. Un successfully.
This woman has harassesd us for years.

Is it illegal for a person to take a letter that is confidential and
give it to another person to try to use to harass or cause some type of litigation?
I mean I did call her a toxic parent. . .but I could also prove that she has a personality disorder that is actually dangerous.
PLEASE HELP ANYONE KNOW IF THE GIRLS PARENTS COULD BE IN TROUBLE FOR DISSEMINATING THIS INFORMATION?