I'm 13 too and i'm in exactly the same position. My parent haven't notice the cuts on my arms or how much time I spend alone now. I found the best thing to make you feel better is to talk to someone who understands what you're going through. Another thing you can try is getting a cheap notebook and writing how you feel and just rant to yourself in your book. If you need to tell someone something but you cant seem to get the words out, you can show them your book. This often helps. I'm usually free to talk and I'll try my best to help you with questions. Whatever you do, don't die. You'll be missed more than you expect.
Hey there <3 I'm 16 years old and was going through the same thing a while back. Isolating yourself will only make you feel more depressed and suicidal. It might not be what you want but hanging with friends or people that will make you laugh or someone you feel comfortable with and are close to makes a huge difference.
I was sent to a depression clinic and trust me did not want to go, I didn't want to have to socialize with anyone or talk to anyone about anything. I found that when it was time for me to go I actually didn't want to leave! :P
I made friends and the nurses made sure we were hardly ever left alone and was actually quite happy.
So try not to isolate yourself and remember that you're worth everything and you are never alone <3 :) xx