In terms of your situation if you want to leave, a question. When you say you've been at uni since 'last September' do you mean September 2012 (i.e. you're a first year), or September 2011 (i.e. you're a second year)? This would make a difference if you wanted to leave your course and then study again at some point in the future - as I understand it, the way student finance is set up allows you one 'false start' year, (i.e. you can get funding for the duration of your course plus one year), so if yu're a first year you would be able to start over elsewhere and get funding for the whole course; but if you're a second year you would have to pay for a year yourself.
That said, if you're absolutely set on leaving, I would propose a middle way - it's usually possible to interrupt your studies for a period of time, which would give you the chance to come back and more or less pick up where you left off, if you later decide to.
My personal view is that I don't see how leaving gets you any closer to where you want to be. If you had a really clear plan that leaving would put you in a better position, then I could see how that would be a good thing, but what you're describing, really, is that you'd go home to be unemployed and be shouted at. Or, maybe, that you'd get a dull job, and still be shouted at.
I am a fair bit older than you, and looking back I had vastly more time and opportunities to do interesting things when I was a student than I have any time since then. Work - even work you do just to make some money to allow you to do more interesting things - eats time; and most of the money gets eaten, too, before you get to do anything much with it. I think there's a real danger of you leaving uni, falling into some boring job, and getting into a similarly unfulfilling routine, just with different geography.
Is your list of 'things to do' absolutely incompatible with being at uni? Are there none at all that you can do now? If you dig around, you may find that there are societies and activities available that relate to some of the things you'd like to try out (and maybe also to socialise with people in ways that aren't just piss-ups).
Also, at uni there are almost certainly support services which may be able to help with how you're feeling. Going along to talk to them might help you to get to grips with things, and feel more comfortable in the life that you're in. I think very often when people feel the way you feel, they want to change things because they believe that a change will make them feel better, and this isn't always the case.
Sorry if some of that sounds horribly depressing! Here's the upside. It is absolutely, 100% OK not to know precisely what you want to do. It's a good thing, in my book; it means you're open to the life you're living, rather than constantly feeling the need to pursue one that's just around the corner, on the horizon, nearly there. You've said that you only have one opportunity to live and you don't want to waste it - I agree with you. But life isn't just one big 'meaning'; it's a mosaic of lots of tiny bits and pieces; some good, some bad. Trying to deal with the bad ones is great, but walking away from them doesn't necessarily help. And actually, you can change the bad bits. And changing them is one of the most useful things you'll do, or learn, in life. Ever.