I've felt as you do in the past, not too long ago actually. Depression is reality for more people that you would think, and understanding what you are going though is not hard to do at all. But I think what you've been doing is underestimating yourself.
When I was depressed, it seemed super easy to simply lose myself to negative emotions. It was so easy to think of myself as worthless, unneeded, stupid, etc. But what I realized most out of all of it was that insulting myself never got me anywhere. It was only when I got through those insults, when I pushed through the depression, that I realized those things I had been saying about myself for so long were all far from the truth.
What I'm trying to say is that depression makes us feel a lot of emotions that we otherwise would not be feeling. It makes you feel worthless and stupid, even though that's not what you are. Try to remind yourself that you are how YOU see yourself - not the person depression sees you as.
It's hard to look ahead of you and think "how am I going to make it through this week... this month... this year?" Don't look at it that way. The only thing that's important is how you make it through TODAY. Sometimes you wake up and don't even want to get up the morning, or even move, but hold your head high and believe in yourself - because you've made it through hundreds of days like this one in the past. If you did all of that, you can get through today.
Dealing with depression is not easy, I know it's not. But each and every one of us have the strength to get through it. If someone would have told me that two months ago I would never have believed them, but now I'm saying it myself. You CAN get through this - no success comes from telling yourself that you can't.
Maybe you need to consider talking to a doctor so you can get some help with this. Depression is a serious problem, and it's not easy to get through it without help. Consider talking to a doctor, it may make a huge difference in your life.
Hang in there, you can get through this!