There are so many times when I feel like a useless piece of garbage because I constantly mess up.
What's an example of you constantly messing up?
Just the other day I broke up with my girlfriend because she wrote that I was her first boyfriend.
You shouldn't allow yourself to feel useless. If you are feeling this down you should seek some help.
What? Therapy is for assholes. I don't need it.
If you're feeling useless all the time then you may actually need therapy, because that isn't a normal way to feel all of the time. A little bit of help has never hurt anyone.