How can I handle the pain I feel when i can barely understand it myself?

I have been suffering from depression since I was in Sixth grade. It's worse now that I am in high school. My depression isn't even about high school or friends or anyone. I come from a very emotional family on my mother's side. I feel the world on my shoulders. I feel, hear, see the pain that people cause each other and I wonder why people hurt each other? Do they do it for sport? I'm always the one to go to for my friends and family and I always care about people, but now I am sick of listening. I listen to everyone, but now when I am struggling to even get up in the morning there is nobody there for me to talk to. It's awful. I know I can talk to my parents or my best friend or my grandma, but they will never truly understand the pain that is in my heart. The pain is unexplainable. I am considered a very optimistic person to a lot of my friends and family, but I don't feel the happiness I felt a few months ago. Now I feel as if all the happiness I have ever felt has been sucked away. A lot of days I spend sitting quietly, I prefer being alone as it has always been the safest place. My mom always wonders if it's friends that I am stressed about, but she is always wrong. She asks what's wrong a lot, but I refuse to tell her my emotions when she is apart of them. My mom is an alcoholic and my family is unhappy and even though I tell her she is hurting the family and hurting me, she keeps on drinking like my words don't matter to her. She knows what's she's doing, She has even admitted that she loves to drink. The only time she drinks is when my dad is working because he limits her drinking because he tries to help her and prevent me from having to deal with my wasted mom every night. Now she drinks even more and now whenever my dad is working my mom drinks, and then I have to babysit her when she is too drunk to stand, forcing me to abandon my school work so she doesn't hurt herself in the process of walking up the stairs. Now it's even worse. She hides her alcohol and lies to me and my brother saying she isn't drinking, but being in the family and seeing the symptomns of a drunk person, I know very well when she has been drinking. The fact that she has to lie because she is so addicted to her beer and wine. I am so stressed out to the point, where I just am quiet, because if i say anything about my emotions, nobody will understand. It's not their fault. They are not the ones in my head, seeing, hearing my thoughts, and trust me I am so glad they can't see or feel the pain I am in. I wish it wasn't so painful every waking second.