How do I tell my mom I think I need a therapist?

First of all Im 13 years old. I'm lonely. I'm nowhere near smart. I only have one person to talk to, but if I say anything like I want to he ends up with a butcher knife against his throat.. My mother and I don't really talk, Im not comfortable talking to her about anything, my dad And I don't even talk, he never use to talk to me about anything. My sister doesn't care, so how do I teller I need a therapist before I do something stupid ? Thank you