Tough love time.
temper tantrums are for little kids. Time to be a big boy and get control of your emotions. You really should be talking this all out with a good therapist. They are trained to teach you how to get a different perspective on life.
RIf you're depressed run 3 miles.. see how depressed you are then.
If you want to be a good person go volunteer somewhere.
You don't have to keep beating yourself up.. if you want to change you can do it but like everything else it's not going to be easy, changing habits takes practice.
All that "I'm not good enough, I'm a scumbag, nobody wants someone like me" is depression talking and you know what..maybe its true but you can change that Shit today if you really wanted to.
go out and do something nice for somebody. See how you feel then.
Good luck