AITA for letting my friend know she was getting cheated on?

This was a while back, but I got my friend together with a guy she had a crush on, and he fortunately liked her back. The two hit it off for a while until I found my friend’s bf kissing another girl in the hallway. I took a couple photos and investigated for a little while before telling my friend that she was getting cheated on. She thanked me for letting her know and broke up with him. I soon later learned that she had gone around the school telling everyone that I was a home-wrecker. Should I have let her find out on her own or tell her regardless of being called said home-wrecker?