Is it illegal for a supervisor to show a co-worker emails I've given the supervisor to show why we did a project the way we did it?

The co-worker is in another department and had no "skin in the game" so to say. I gave the string of emails only to my boss and had no idea she would let another employee read through them, nor do I know why my boss did this. I believe my boss was trying to find if I had done something wrong or without the proper permissions on the project (which she did not find because I clearly had followed standard protocol and had the necessary permissions). The co-worker seems to be a confidant of my boss and worked, at the time, with another employee who was a part of the project in question that I was coordinating and I've been told my boss was "gunning" for the guy. he has since resigned but I am still here and feeling like it was inappropriate in the very least for my boss to show another employee, in another department, my emails. Is there anything illegal about what my boss did?