The feeling of loneliness is likely the basis for "I missed you." Forlorning. And it's noticed during reflection, alone.

We grow up in schools, where we've known 60%+ (of our class) since 1st grade (or earlier), and now -- in adulthood, we're thrown into a world full of strangers, everyday strangers. Friends help, but it doesn't mend that community we had in our day-to-day school work.