You made a mistake, you fell off the wagon, you let someone down, you let yourself down — but it isn't the end of the world. You are still the same person you were before you let this fear of not being good enough wash over you.
You deserve so much more than you allow yourself to believe, just because you have hit a rough patch doesn't mean that you are unable to bounce back from that.
If you are currently fighting through something and are not sure how to come back from that, let me tell you that you are never alone. Someone, somewhere, is waiting for you to need them. Maybe it isn't your family, and maybe you don't want to "bother" your friends (which is crazy to think. That's why they are your friends!) but there are people waiting in chat rooms, facebook groups, and on the other end of your phone waiting for you if you need them. They want to be there for you, so let them be.
Never doubt that what you are feeling matters or that there are people out there just waiting for you.
Another thing that you need to remember is that you are only temporarily going through this. This pain you are feeling won't be around forever. You are going to grow from this, and this will be a meaningful lesson for you later on in life. You can't have a rainbow without a little rain.
Lastly, you are stronger than whatever is hurting you. Think of all of the things you have gone through up until now. You have lost family members, friends, maybe even a job, and you are still strong and handling everything that life throws at you.
Don't let this be the thing that breaks you — you may not be at your best right now, but that just means that your best is yet to come.
Make life yours, and you'll see that the pain you are going through now is nothing compared to the joy you are going to feel later. You deserve more than you are settling for, let yourself heal from this and you will be the best version of yourself in no time.