In my experience, this is quite often the case; I have a very close friendship with somebody for two-three years and then they move away/move on in their life. Or at least that was the case earlier on in my life; there are a handful of people who I regret not having made more of an effort to stay in contact with, but these days I do all I can to keep in touch with everyone. It’s an unspoken promise that I make to them and to myself.
Ultimately, I find that people still move away or move on with their lives after two or three years, but by keeping in touch, I still get to hear from them online and see them from time to time, which is a bit sad, but infinitely better!
(Read this post on my new site.)