Rarer still are the true forever best friends, those who are by your side for decades on end—through jobs, moves, relationships, fights, losses, and life stages—and may even come to feel like family.

Rachel Schroeder and I have been friends for 43 years! We met as freshmen at DePauw in the Bishop Roberts dorm in 1982. I remember sitting in the hallway, eating popcorn with everyone on the floor. I ...