I'm sorry you are feeling so crappy. I understand how miserable you are and it stinks. Have you seen a doctor for your depression? I've been going through this for a few years - not as long as you, and finally seem to be coming out of it, though I'm still having my ups and downs.
I think your friends might be avoiding your because they don't understand what is going on and don't know how to react to your moods. For people who haven't been through depression, they just really don't get it - but it's not their fault. Perhaps if there is one or two of your friends that your trust, you could open up to them and explain that you don't understand why you feel so low, but you would really appreciate their support.
I have been on a combination of meds and seeing a psychologist and psychiatrist over the last 3 years or so. I've had times where I felt life wasn't worth living - but when I'm feeling OK, I know it definitley is, and that the people in your life would be devestated if you did anything to hurt yourself, or more. You really need to open up to them so they can understand and help you through this.
Hang in there, and please get some help from your doctor. If you can, keep going to school, even if you cut down or defer part of your subjects, socialising is really important - the more you isolate yourself, the worse you will feel. The anger is part of the depression.
Take care and let us know how you are going.