Sometimes...

You have to move on, you have to admit to yourself that people have changed and are better off with other people, in other places.

It's a sad, hard fact of life.
One I've personally faced time and time again.
You need to move on for your own good.

Let me tell your something:- As one person walks out...another walks in.
Yes it hurts, yes it's upsetting, but you must be strong in order for this to happen.
Enough is enough, your friendship is deserved by someone else, just as someone else's friendship is deserved for you.

Yet for that to happen, you need to start wandering down the path that leads you to that person.
Soon, the hole and impact that was left will slowly mend, it won't go away but it will be better, as you'll have someone else.

Simplified version:-
As one leaves, another enters.
That simple fact applies to most- if not all-areas of life