I'm going to run away tonight
Why would you run away ?
I'm scared of the dark but I don't like living with my parents, I'm sick of it.
If you're an adult, you are legally free to leave your parents whenever you want. But you have to be ready for all of life's challenges to hit you at once, and I hope you're ready and don't end up homeless.
I don't think I'll end up homeless. We talk about it later.
If you wish to live by yourself, you're free to do so. Still I'd suggest you to think through this and make the right decision.