I'm going to give the long version.
So my girlfriend made friends with a guy (We will call him Paul) that went to the college across the street from the gas station that she worked at. She slowly introduced him to the rest of the group of friends. Paul grew to like my girlfriends friend (Ann). Paul considered Ann his best friend, even though Ann felt creeped out by him most of the time. Paul moved away back to West Virginia because his father died. He told Ann that he uses a pacifier or bottle, basically leading up to telling her that he's an AB. After he told her that he wears diapers she told everyone. She freaked out when she found that out about him. Whenever she gets a snapchat from him, she asks everyone if they think that its going to be him in a diaper. She screenshotted a picture of him wearing a diaper to show everyone as proof. I already know that she has told our group of friends. Which is about five people. And I don't know who else she has told. I feel bad for the guy. I never got close to the guy because I got the impression that he was into me when I am not gay.
Should I tell him that the person that he trust the most is going around and telling everyone about his ABDL side or is it better not to tell him and ruin trust that he has in her/possibly everyone he's told?