You get told a lot at certain points in your life that you'll lose the friends you currently have and make more in the future. I remember graduating middle school and being told I'd make my true "life long" friends in high school. Then, upon graduating high school, I got told the same thing about college. I haven't graduated college yet, but I'm already hearing things along the lines of "you'll find life long friends after college."
I think the biggest thing I've taken from this is that everyone's friendships are different. There are people out there that maintain friendships from the time they're born, which is extremely impressive. I'm still friends with my kindergarten best friend, even if we talk sporadically, we do still talk. I'm also still friends with my first grade best friend, and we talk much more frequently. And I talk to most of the people I talked to in high school still. Our lives are different, we're living in different places, but I care a lot about those people. I still want to know what they're up to, and I just don't have it in me to let those friendships fade without putting in all the effort I can to maintain them. (Of course, it's a two way street, so they have to help me with that. And I'm very lucky to have friends that do.)
None of that is to say I haven't lost friends. Believe me, I have. There are people I was extremely close to as a kid who I don't talk to much anymore. I just found out one of those former friends is getting married soon, actually, and I was clueless to it. So I have the former friends whose lives I no longer know nothing about.
A couple of them just drifted away, but for the most part, I aided that pulling away because I came to the realization that I couldn't have them in my life for various reasons, ones I won't rehash here. When it comes to my friendships that are very valuable though, the friends who have legitimately been there for me through a lot, I can't move on past that friendship, not unless they give me a reason to.
These people have meant far too much to me for me to just let us grow apart, and I think that's why the idea of it has always terrified me. I've lived in perpetual fear of it happening. But I've got to realize that if such a thing happens it's for a reason. First of all, the fact that I'm working against it already diminishes the chances. If I'm doing everything I can to maintain a friendship yet we grow apart anyway, that's probably a huge sign that that friend didn't care about me as much as I did them, and in that case, it's probably best that we are no longer friends.
But with the friends who truly matter, we'll always maintain some form of friendship, even if it morphs and changes as we do. I can go a year without seeing my older friends in person, but when I do manage to see them, it's always abundantly clear why they've stuck around so long in my life. Because each friend contains another point of my life, and even if we're changing, what they did for me at that point in my life is extremely valuable. And each of them continue to be important in my life in various ways. They're still supporting me even if it's from a distance. I know each of them care, and each of them have proven again and again that they will legitimately be there for me when I need them. No matter how much older we get, that never seems to change with these friends, and for that, I am extremely thankful.