Hi Kiki
My heart goes out to you.
I can relate to all the things you are saying because I felt like you at your age. (i am now in my early 50s). I completely empathise with your feelings of fear, your lack of confidence, your self harming. And my heart goes out to you.
Also at your age, things changed for me, and I believe that things can change for you too so that you will, eventually, see that you have worth and value, just for being you. I know that might seem impossible now, but it has happened to me, and it can happen to you too.
I believe that your outpouring on here is the 'real' you, the you that wants life, the you that will bring you through this. I also don't think its easy for you to see this now, but, trust me, this is the strong inner real you.
In my case I discovered, through many sessions with and support from an excellent psychologist, that my problems lay within my childhood. Another poster has also suggested this, and this was certainly my experience. It took me a long time to even start to accept that my utter lack of self worth might not be to do with me, but was rooted in the events of my childhood, and especially in my very problematic relationship with my mother.
In retrospect, I have realised that my extreme depression was somehow a 'safer' way to be than trying to face up to the problems with my mother. I don't know why, but it was.
I don't know if any of this chimes with you.
You coming on here, and writing here, shows to me that somewhere inside you you need and want to carry on, but carry on differently to the way you feel now - how to get from here to there is why you're writing: to look for ways forward. That's why people see you as strong. You do have real inner strength to write here, to reach out, to be honest, and that is so hard to do especially when you are feeling so low.
X