You have to ask yourself what is a true friend. And when your friends let you down are they worth keeping? How good of a friend were they anyway?
I have several examples of crapy friends.
First would be of witness friends after my mom died. No one talked to me of course and I had to grieve alone. I'd call them crapy friends.
Second is friends that owe me money and never paying up. Some ppl just feel entitled. Selfish.
But what can you forgive or put up with? I find myself staying friends w/lot's of ppl that owe me money although it annoys me.
We are all human and make many many mistakes. I'm not perfect and I know I haven't always been a great friend. So if I want forgiveness and expect it, I should forgive those who let me down. Right?
Every situation is different. It's ultimately about what you can deal with and how much disappointment you can stand.