Siccness, I know what you're going through, broke up with my girlfriend in March & hit rock bottom.
While I'm defo not a specialist, still struggling sometimes & our problems/substances are different, first thing don't be ashamed of your issues, they're part of you. But don't think too much about them, ok you'll have to sort em out but remember there's a whole world out there, great people & gorgeous girls to meet, and a life to live.
You gotta regain some self confidence. You're really young. Younger than me! Even if you really don't feel like it, force yourself to go out, check out whats going on, go to gigs,etc... you're bound to meet a few people, who might be nice, might be twats, but who'll take your mind off your problems for a little while at least.
Don't think of yourself as just a depressed druggy - these are your problems, not your whole personality. Try pulling some girls, even if you don't really fancy them - I know it sounds dopey and corny as fuck but it worked for me - cos when depressed, getting laid, whoever with, always helps a great deal, good outlet and boost your confidence.
If there's something you're good at, be it music, sport, writing, whatever (not drugging and drinking!), I suggest you do it as often as possible. You're worth a lot more than you think. Find little things that make you happy, like listening to a certain song at a certain time of the day, and try to find out how & why they make you feel that way, so you can find more things to do to make the day a bit more fun to go through.
Sorry if it sounds really basic & not exactly subtle but I've been through the same shit and these tips really helped; suffered from depression & was a hopeless alcoholic since I was 14, and felt pretty much the same as you are feeling now, and thought it could never get better. It does get better. You have no idea how great life can be, you still have so much discover even if you think you've seen it all, believe me. We're all different but give it a go, just to see. I wish you the best of luck man, there'll be better days.