What did you think all our conversations were about?
What did you think all our conversations were about?
「今まで話してきたこと、何だと思ってたの?」
conversation は「会話」という意味です。
例文:
We were talking about chocolate the whole time, so what did you think all our conversations were about?
「ずっとチョコの話をしてたのに、今まで話してきたこと何だと思ってたの?」
お役に立てれば嬉しいです。