Actually, he was right, and your version is incorrect. “I was the only one who…” On the other hand you’d be correct in a phrase like: “The only people who we

Actually, he was right, and your version is incorrect. “I was the only one who…” On the other hand you’d be correct in a phrase like: “The only people who were cheated were his brother and me.” The word me is an object of a sentence, not the subject.