It happens, and it happens out of all kind of reasons. You will know how much you meant as a friend to them in the aftermath by how/if they speak about you.

For various reasons.

Sometimes their lives take different directions in life,so they just drift apart over time

Or their ego is stronger than their friendship ,so neither make the first move to salvage the friendship whenever issues arise. .

One is punishing the other for who they aren't.

Well to be honest, I'm still trying to find an answer as to what friendship is really supposed to meant. I was a very loyal friend to a lot of people out there. Always doing as they wanted and however they wanted things to be done, accepting them unconditionally, helping them with whatever I left them believe they need help with. But over time, each and every one of them was taking advantage of this loyalty and expected more and more things to be done with no consideration of my time whatsoever. I felt overwhelmed and pressed, because they brought their pressure to a point where I couldn't even say what I thought was right.

One by one, I had to stab them all in the back to get rid of them and gain my free time back. And in one day, I left all fifty friends of mine in real life. And the confrontations, they were brutal. I had a lot of nightmares for a while after that, but the crisis is over.

We outgrow people. We are meant to. Not all, but most.

Usually its bec someone thought one thing while the other person something else, without checking

I am moody

Halitosis

People change. We evolve, we grow. Sometimes our friends grow with us, sometimes we grow apart.

Every relationship has a breaking point..
Same reason marriages dont last...

Theres a grab bag full of answers for that one... unfortunately it's out of my reach!

I would like to know the answer in a couple of old best friends. They just refuse to talk.

If i knew that, i'd have all my old friends back.

Even you stop talking to me. 🙄

We all realised I'm a horrible person and I moved away.