When it's time to unfriend

We all get to that point.  We have a friend on fb that we actually have connected with. We consider them a friend, just like any friend we make in real life. But for whatever reason, things go wrong.
Now, a lot of us make a lot of friends on facebook. At times we have to cut our numbers,  and when we go searching we just cut the ones we never connected with. Those are easy. Simple friend management. Nothing more. Nothing less. In real life those ones just fade away,  like high school friends you knew for a year but never had any contact with for 20 years,  or neighborhood kids you might have played with but drifted away from as you both got older.
But then of course we get to the ones who were/are still close friends. Or so we thought. 
How does it get to that point? What happens to break the friendship and make us decide to possibly delete them..or not?
What was once everyday contact dwindled. What were always quickly returned private messages are now not answered. Is it simply a case of bad timing? Or are they sending you a message?
You just don't know. Your inclination is to delete them. But you don't want to. Not that way. You feel like you want to give it a chance.
So, you resist your urge to cut them, and wait a while. You kind of hope they will just put their hand out and reconnect. But they don't.  Another month passes and you start thinking about deleting them again. But you don't want to. You have put so much time, effort and emotional investment in the friendship that you want it to be repaired...to go back to how it was. Do they feel the same way? You don't know. Or at least you are unsure.
Should you send them some sort of email,  asking them where you guys are at? Do you come off looking like some sort of drama queen by doing that? Do you care if you do? You probably do and you resist that temptation. For now.
Of course, in many instances it hurts,  at least at first when you realize it is probably not going to work out. Just like a romantic relationship. You know, intellectually that it is for the best, but emotionally that doesn't register. 
As time goes by, you realize you have to defriend them, because..they simply aren't your friend and you are fooling yourself if you think they are. And that is almost always proved out by the fact you defriend them and they don't even notice..or care.
It is always a tough call, but usually if you think you need to defriend them,  you do.