Ok, before I say anything, let me apologize ahead of time if people are offended by what I'm about to say. Unlike others, I'm not here to coddle you.
I've been depressed before. My boyfriend's been depressed before. I know the easy, politically correct thing for people to say is you can't help it. But the reality is YOU CAN HELP YOURSELF.
Here are some options for you right now.
(1) Seek professional help. Like right now. Not next month.
(2) Stop doing what's comfortable. You can help yourself, but you have to do things that are outside your comfort zone. For instance, you may feel like crying at the moment. Force yourself to smile. Force yourself to cheer up. Force yourself to laugh. You may feel like you want to be alone. Force yourself to be in the presence of other people. Force yourself to get into a relationship.
YOU ARE NOT HELPLESS. All the people who want to coddle you are pretty much telling you you are helpless.
Back in college, there was a time when I fell into a deep depression. It made me fail 2 classes. I was in the library one day and stumbled onto a book. Can't remember the title or who it was by. But the author made the argument that depression can be treated by the depressed by going against how they feel. I tried that and it worked like a charm.
Years later, I met my boyfriend. He also struggled with depression at times. His doctor put him on anti-depressants. It worked for a time, but the side effect was it killed off his sex drive. We didn't do anything for months. I think I made a thread on here somewhere complaining about that last year. Anyway, after a while, he stopped taking it and one day when I came home from work he jumped on me and we made love for an hour. He then went on my method. It wasn't easy at first. He struggled, and it's completely understandable. He had to force himself going against what he felt like. Once he got used to it, he felt a lot better.
I know you don't feel like smiling. Force yourself to smile. I know you don't want to be around other people. Force yourself to be around other people. Get a boyfriend. Do whatever it takes to make life better for yourself.
Remember YOU DO NOT HAVE TO BE HELPLESS. Help yourself, for goodness sake. Either that or give up on life. Your choice.
Edit.
Here is my evidence that what you do physically affects how you feel.
http://www.scientificamerican.com/article/smile-it-could-make-you-happier/
I know it's hard to go against how you feel. What people need to learn is the reverse is also true. What you do affects how you feel. If you feel depressed and do things to make yourself depressed some more, you're just putting yourself in a perpetual cycle of depression. Go against your instinct for once and take a step outside the perpetual cycle of depression.