You have someone that yo been friends with for many years, through good and bad times, then “poof” nothing from them. Emails and text messages go unanswered, phone calls never returned. The person is still alive and okay, social media can be a good and bad thing at time, but for whatever reason has decided not to communicate with you any longer.
Something you said or did? You would hope that a true friend would tell you when something upsets them. Moved on in their life to a different spot? Maybe, but seems like you would expect the “courtesy” reply now and then.
Not much you can do but go on with your life, and wonder from time to time.