Boyfriend Scolds Me for Rivaling His Childhood Friend, But He's Male

After my acceptance letter came through, my childhood best friend, who'd repeated a year, got into the same university as me. The day before the semester started, I invited my boyfriend and my best friend to play a game together. My boyfriend picked a marksman, and the second he did, my best friend locked in support, then typed: "You have to protect me, big brother." "Big brother, I'm about to die, save me." "Big brother, you're so amazing!"