I’ve been thinking a lot about friendship lately: How one person can weave in and out of your life, withstanding the tests of distance, time and change, while another can just disappear.

I miss the disappeareds.

I had a friend in college named Sally. She and I met during freshman orientation. We survived the rush of new-friend adulation and learned to pardon each other’s quirks and faults. We spent snowy afternoons together and Friday evenings together and weekends at each other’s homes. We entertained my parents when they came to visit with tales of college boyfriends and errant professors. She was my best friend.

Sally and I kept in touch for several years after graduation. Then …

… nothing.

The disappearance wasn’t wholly unexpected. While she grew into maturity gracefully, I made some seriously compromised decisions. The last time we talked — as I broached yet another questionable choice — she cut the conversation short.

I never heard from her again.

I’ve reached out over the years. I sent her an invitation to my wedding. A letter when my son was born. I could send her a Facebook friend request (yes, I’ve looked her up). But why risk the silence?

My memories of Sally rekindled this weekend. I went to Kansas City for a short visit with my parents and spent some time with my old college roommate.

L and I had a similar trajectory as Sally and I: Constant contact in school yielding to long-distance correspondence. A graceful path of maturation (her) pushing against a flailing mess. But she didn’t disappear. We hardly see each other anymore but when we do, it’s as though no time has passed.

Why did one person go and another stay? Why did one make allowances for a friend’s poor choices, while the other cut her losses and ran?

My mother says this isn’t about me. She reminds me that we never know another person’s story — that Sally’s disappearance may have had nothing to do with our shared past and everything to do with her unique present.

Still, I miss her. I wonder what her life is like now: If she still has her killer sense of humor and why-not-try-it attitude. If she still makes people laugh with a twist of her mouth. If she still cuts through artifice to a matter’s (or person’s) heart.

I’ll never know. I’ll have to be content with my memories of a lovely friendship.

Yet while I celebrate those memories, I’m making a promise to myself. I promise to value my friends today. I promise to diligently celebrate them, whether their friendship is new or polished by time. I promise to check in on them, keep tabs on them and allow for their mistakes and foibles.

I promise that they won’t disappear.