This is called a relapse.
When you relapse, you fall back into the same state of being that you were once fighting against. Relapse almost seems like the opposite of recovery, but I think relapse is actually a part of recovery. A pothole in the road isn't the opposite of progression on a path, but rather, a part of it.
I know you might feel like a failure after you relapse. But this is where you have to fight. This is where the negative and self destructive thoughts try to take over. Don't let them win. I know its hard sometimes, but its worth fighting for .
I know you want to blame yourself; I know those voices in your head are throwing all sorts of lies and insults your way. I know you feel like you have failed yourself, or the ones you love; but there is grace. Oh, is there an abundance of grace. Did you know that God loves you, even when you relapse? Even when you're in your destructive cycle, His hand is ever present, reaching out to you to help you. He wants you. Right here and right now. He doesn't want you to go clean up your act first; He want you now. In all your filth and shame. He wants you even though you have relapsed. He has grace and love for you, and He wants you to have grace and love for yourself too.
Even though you have fallen, I know you can get back up again. You have been knocked down, but not knocked out. There is hope for you. In the midst of relapse, it can feel like its over; like you're stuck with no hope of ever escaping. But you will rise. You will not be here forever. Recovery is probably the hardest thing you'll ever do, so its going to take some work and you're not going to get it perfect; and when relapse comes, you must forgive yourself, and know that its okay to fall and believe that you are strong enough to stand back up again.
I believe in you. I really do. I believe that some day, you will beat this. You may relapse 5 times or 500 times before you make it; but you will make it. You're a fighter, you always have been and always will be. Today is your day. You might not see the point in trying to recover, but there is a point and there is a purpose. You have a purpose. You will recover.
Stay strong little fighter.