Hmm...Well, first of all I want to say I was going to post my usual stuff as I was reading, but then I read the bottom. I want to say thank you for being respectful about it and not laughing at my beliefs. However, if you don't want religious advice and you're sure that you don't need faith in another being, I would suggest not saying you're agnostic, and just go with atheist. Agnostic means you're not sure; atheist means you're definite. Fortunately, I can work both ways, God-related or otherwise.
Now, with your problem. Easy enough, you're depressed. Any non-doctor can tell you that. Rest assured that depression is a temorary ailment. How long "temporary" is, though, is the problem with it. Could be days, months, years... G-d (sorry, just joshin' ya!) only knows. Not to make this about me, but I've had it last anywhere from just an hour to about a year. So, yeah, just to give you an idea...
How long have you been experiencing this hopelessness?
Did it start in your teen years or younger?
Did it start only when you realized how soon high school will end or has it been a periodic-type thing? Or are other issues (even minor problems that you may not think are problems) going on concurently?
Answer me these and maybe I can give you some idea as to what your problem may be and better help you solve it. To encourage you a bit, depression is usually found in the most brilliant, creative people. Unfortunately, I've not found a way to "pull out" of depression like magic. But, somethings I've found that lift me up during depression, though, are:
-relatable music (I like Emilie Autumn's "What If", "Misery Loves Company", "Shalott". Really, any of her music is good.)
-really funny stuff (read the blog Hyperbole and a Half, watch hilarious cartoons or other shows)
-and getting in touch with your childhood (watching "The Little Mermaid" or "Toy Story", looking through pictures of your childhood).
Hopefully, that'll be of some assistance to you. Anything else you may want to know, I'll be happy to help you with.
Just because everything's changing
Doesn't mean it's never been this way before
All you can do is try to know who your friends are...