Double post sorry
Why not just be honest with this person instead of talking about them behind their back? (Rhetorical questions).
I feel like both parties are in the wrong, and I think both should apologize in my opinion.
This is tricky for me, because I am typically a very nosy person, and I have no self control when I'm given the opportunity. There have been times when I stumbled upon stuff by accident that my friends or my (ex)SO was talking about me, and yes, I was very mad because it hurts.
My ex kept a journal, but I didn't know what it was. We lived together and I just randomly found a notebook sitting there, and when I opened it I saw my name. So obviously, I read. Every single entry was him talking shit about me. Needless to say that didn't work out well.
Another time a friend let me on her FB to do something, I can't remember what, and she had a message pop up from one of our other friends, and they were talking shit about me. I guess she didn't realize if I was on her account on my computer her messages would still show up? Pretty shitty.