When we accidentally saw my fiancé’s ex at an event, my brother suddenly started acting as if he knew him. It turns out they’ve known each other from a distance since childhood, but they haven’t spoken. While I was still processing this, my brother tried to joke around with my fiancé’s ex and act like he was someone we knew. My fiancé was silent, but I was pretty tense. What should one do in a situation like this? Should I ignore it or talk to my brother? Have I been too sensitive?