Acquaintances or Friends?

I have this issue with categorizing people as either friends or acquaintances. There are people in your life who clearly fit into either one of the two categories, though, there's more often than not that group of people where you're just not quite sure, are they your friends or your acquaintances? How do you distinguish between the two?

I have this incessant need to categorize the people I know into these two groups. I would love my acquaintances to become my friends, but how do you know if you're acquaintances are just as keen in becoming friends? And how do you know when you're acquaintance has become your friend? Is there some type of threshold they would have to pass?

I'm most likely overthinking this. From experience, I've figured that an acquaintance usually transitions into the friend stage at the point when a)you exchange phone numbers; then b) suggests to hang out sometime; and c)actually hang out. The tricky part though is remaining in contact. If both sides of the friendship do not make an effort to remain in contact then that friendship dissolves and soon you become mere acquaintances. Which is such a shame when you think about it, because you lost a potentially good friendship because you were too lazy to maintain contact.

About two years ago I worked full time for the summer months, and during those short 4 months me and four other girls at work really bonded. We spent our lunches together, our breaks, partook in work gossip, and basically had a good laugh everyday. Two years on and I'm glad to say that I'm still in contact with 2 of these girls and we have a bi-annual reunion with four of us. Though there's that one girl who is now simply an acquaintance, she never responded to the reunion invitation, and after that we simply stopped inviting her. It's unfortunate because from all the girls, me and her spent the most time together at work, and now I wouldn't even think about messaging her, as I fear potential awkwardness. Potential awkwardness, that is a good topic for my next post.