Why did I have to let everybody down!?

I don't know what happened, but I hope you feel better.
If you have done something to others that made them sad and its your fault, then try to apologize to them. Only actions can make guilt go away.
If you did not do anything wrong, then it's okay. 
Here is a quote that made me feel better and heard:
https://www.instagram.com/p/B7SBh6Clo2z/
I hope it helps you.

You're aware of your shortcoming or failure.  Now you can learn by that, and be positively motivated by your remorse.  It is likely some of the people continue to love you, and will forgive you.

Related:

https://www.hopefortheheart.org
http://klove.com 1-800-525-LOVE
https://www.mothermeera.com
"Understanding Yourself" by Mark Prophet;
"101 Things All Young Adults Should Know."

Stop whining.              

you're self destructive?