Time is how you find out which friends were real. It filters without you lifting a finger.

Some connections need constant maintenance to exist at all, and some survive long gaps without effort from either side. You cannot tell which is which in the first year, and no test would tell you. Time sorts them without needing your participation, which is a relief and also a loss, since the sorting is not always in your favour.

You do not have to audit your friendships. Just notice, over a long stretch, who reappears and who you reach for when something happens. Put your effort there. People drift for reasons that usually have nothing to do with you.