I'm sorry to hear that you're feeling numb.. That's the worst "feeling" I think.. not being able to feel anything related to the people you care about, the world, anything, really.. It is terrible.
That how I've felt when my depression has been really bad.. I'm sorry that's where you are at the moment. Have you gotten any treatment in the past? You mentioned therapy. Are you still in therapy? I've tried different therapists, but I've found someone now that is helping me a whole lot. Don't give up on it.. If you don't think you can connect with your therapist, try someone else.. And it may take some time as well, unfortunately.. so don't give up on it just yet..
Please don't say that you're a mistake. You're not a mistake and you're not disgusting. You're a wonderful person, a very caring person it sounds like to me. Who cares about her friends and wants to be part of this world, but who is having a really hard time right now.. Struggling is not a mistake. Being bullied is not a mistake, it's a terrible thing to experience. And you have reason to be proud for existing, for posting here, for reaching out. That's hard to do, but you're doing it. Great job!
About self-harm.. I'm sorry you feel the need to hurt yourself. Have you talked to someone else about it? I think it helps to work on it with a therapist. They may help you to find other ways to cope when those urges come about.. I've struggled with it a bit, and it's hard to stop doing it, but it is possible..
Even if it might not feel like that now, the world can come back to you. The colours, the connecting to others, the tasting, sensing, experiencing... I wish I could take your hand and drag you out of the fog you're in at the moment..
Try to connect to the world in small ways if you can.. Focus on sensing things, on feeling the warmth of a coffee cup, look at a tree, a leaf, the sunlight, a candle.. listen to a song.. Sometimes finding some way of connecting can help a bit.. Do you do any arts now? If so, try to do a bit of that if you feel up to it. It may help.. And keep posting here.. We're here with you. You're not alone..