People don't all define "friendship" the same.

In order for me to consider someone a friend, we have to at least communicate on a regular basis and provide each other with mental/emotional support. To me, this is the type of thing that doesn't last forever, if it ever actually existed in the first place. The majority of people get married and/or have kids, or someone moves away, and you just aren't that priority to them that you once were. You'll barely speak, and if that's the case then the mental/emotional support is also not really happening because things happen to you more than once every 6 months or however often you two talk and "catch up."

I've never believed in friends forever. I grew up with a bunch of fake friends that I now know were bullies because that's how they're labeled nowadays (female bullies differ from male bullies in that a lot of them pretend to be your friend), and I also grew up with a mother who constantly told me "there's no such thing as a friend." By my definition of a friend and friendship, I've had at most four real friendships throughout my life...and only one of those lasted for more than a few years, and that's the one out of all 4 that I'm debating most about did I get enough support from that person to even say she meets my definition.

I bring up how people define "friends"/"friendship" because so many people use those terms loosely. And if you're just easily handing out the "friend" label, then you shouldn't be surprised when those "friendships" don't last.