I've struggled with this before my self, where I would run a disastrous session and feel like shit about it for a while after. It happens to all of us, it's not a personal shortcoming- We all make mistakes, and your friends aren't mad at you, and they understand you. 
My worst sessions ever are seared into my brain.
But hey, I'm still here, running the best games of my life lately, especially now that I'm trying rules-light games instead of DnD