My girlfriend made a joke about a special memory of mine

My boyfriend made a joke about something personal that I had told him before during our date last night. His friends laughed, and I literally turned red. Then on the way home, he said, 'I was just joking, why are you taking it so seriously?' But you know, I feel like some things need to stay private, right? Do you think I'm overthinking it, or is this really a boundary violation?