I guess he and his best friend trauma-bonded during high school, and it’s made them close. Whenever we go on dates, he keeps his phone on alert to make sure nothing bad happens to his best friend. When we’re over at my place, he shows me pictures of him and his best friend in high school. Once, he even brought up his jealousy over his best friend and his ex-boyfriend WHILE WE WERE ON A DATE. I’m also fairly sure that his best friend has feelings for him, and that he’s aware of that.