Honestly, it's just not possible you're a failure at the tender age of 18. You're still literally developing and growing-up. You're still figuring out yourself and the world around you.
Based on what you have shared (feel like a failure, lack of self-control, unable to finish things), it sounds like you have depression. Do you have access to medical care? A doctor? I really encourage you to talk to a doctor and tell them what you've shared here. Depression is a mental health issue and there is help available.
Reminder: you are not a failure! You are a growing, developing human being filled with potential. You have options. There is hope.
I'm really glad you found your way here. I hope you continue to share with us if that helps you. We are here for you.
Sending hope and strength to you.
RAGE